Eye tracking system

ABSTRACT

An example eye-tracking optical assembly includes a light source for illuminating an eye, a first diffraction type polarizing beam splitter (DT-PBS), and a second DT-PBS, wherein the first DT-PBS is configured to direct, based on polarization, a first portion of light from the second DT-PBS towards an eye-tracking detector.

TECHNICAL FIELD

This disclosure generally relates to optical elements and opticalsystems implemented in various types of electronic systems and devices.

BACKGROUND

Liquid crystal on silicon (LCoS) active-matrix devices are miniaturizedreflective devices using a liquid crystal layer on top of a siliconbackplane. LCoS can be used for spatial light modulation, wavelengthselective switching, structured illumination, and optical pulse shaping,as part of the illumination system for projection televisions andnear-eye projection displays, among other applications. LCoS systemsencode spatial information (e.g., display information) as a phase delayto the light in a pixel of the LCoS active matrix by applying electricfields across the liquid crystal of the LCoS pixels.

SUMMARY

In general, the present disclosure is directed to optical assembliesconfigured to direct polarized light. The optical assemblies may be usedin, for example, an LCoS projector, an eye tracking system, or the like.For instance, the optical assembly may be used to extract and directpolarized light from the projector light source to an LCoS display andfrom the LCoS display to an optical combiner. The optical assembly mayinclude two or more directors of light, at least one of which is adiffraction type polarizing beam splitter (DT-PBS) that splitsunpolarized light into two beams with orthogonal linear or circularpolarizations and directs each beam in a different direction. Thepresent disclosure provides optical assemblies based on DT-PBS's whichinclude polarization sensitive gratings such as transmissive andreflective polarization volume gratings (PVGs), Pancharatnam-Berry Phase(PBP) gratings, liquid crystal filled surface relief gratings (LC-SRG),holographic polymer dispersed liquid crystal (PDLC) gratings, or anyother optic that can direct a first and a second polarization state indifferent directions, or redirect a first polarization state withoutredirecting the second polarization state. Diffraction type polarizationbeam splitters have the advantage of being thin and lightweight,allowing small form factor LCoS systems not possible using conventionalpolarizing beam splitter cubes. In addition, diffraction typepolarization beam splitters can be designed in pairs to compensate fordispersion.

In other examples, the present disclosure is also directed to an opticalassembly for directing light to an eye tracking detector afterreflecting off an eye. Diffraction type polarization beam splitters,because they are thin, lightweight, flexible in design and cancompensate for dispersion, enable alternative form factors and the useof broadband illumination for eye tracking, e.g., LEDs.

In some examples, DT-PBS can extract a portion of light having a firstpolarization state and redirect it in transmission, for example intodiffraction grating orders. In other examples, the DT-PBS can extract aportion of light having the first polarization state and redirect it inreflection, e.g. redirect the light to exit the DT-PBS through the samesurface as which it was incident on the DT-PBS, for example intodiffraction grating orders in reflection.

In some examples, the first and the second split polarization states areorthogonal. For example, the DT-PBS can redirect by transmission orreflection, the first linear polarization at a first angle and transmitthe second, orthogonal linear polarization, e.g., the linearpolarization state rotated 90° with respect to the first linearpolarization state. By way of another example, the DT-PBS can redirect,by transmission or reflection, the right-handed circular polarization(RCP) and transmit without deflection the left-handed circularpolarization (LCP), and vice versa. By way of one more example, theDT-PBS can transmit and redirect light of both right circularpolarization (RCP) and left circular polarization (LCP) in differentdirections, e.g., in different diffraction orders.

In some examples, the disclosure describes an optical assemblycomprising: a display, a light source for illuminating the display, anda first DT-PBS configured to direct light from a first light director,wherein the first DT-PBS is polarization sensitive and configured todirect, based on polarization, a first portion of light towards thedisplay.

In some examples, the disclosure describes a head mounted display (HMD)comprising: a display, a light source for illuminating the display, afirst DT-PBS configured to direct light from a first light director,wherein the first DT-PBS is polarization sensitive and configured todirect, based on polarization, a first portion of light towards thedisplay.

In some examples, the disclosure describes a method of directing lightcomprising: directing light from a light source to a first DT-PBS by afirst light director; and directing, based on polarization, a firstportion of light towards a display by the first DT-PBS.

In some examples, the disclosure describes an eye-tracking opticalassembly comprising: a light source for illuminating an eye; a firstDT-PBS; and a second DT-PBS, wherein the first DT-PBS is configured todirect, based on polarization, a first portion of light from the secondDT-PBS towards an eye-tracking detector.

In some examples, the disclosure describes a head-mounted display (HMD)comprising: a light source for illuminating an eye; a first DT-PBSconfigured to direct, based on polarization, a first portion of lightfrom a second DT-PBS towards an eye-tracking detector.

In some examples, the disclosure describes a method of tracking oneand/or both eyes of a HMD user comprising: directing light from a lightsource towards a user's eye; reflecting the light from the user's eyetowards a first DT-PBS; directing, based on polarization, a firstportion of the light from the first DT-PBS towards a second DT-PBS; anddirecting, based on polarization, the first portion of the light fromthe second DT-PBS towards a detector.

Thus, the disclosed examples provide an optical assembly that can belighter, thinner, more compact and allow for a broader range of opticalillumination sources and projection paths in a display projection systemthan conventional polarizing beam splitter cubes. Furthermore, thedisclosed examples provide original and effective solutions foreye-tracking systems.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration depicting an example artificial reality systemthat includes at least one diffraction type polarizing beam splitter, inaccordance with the techniques described in this disclosure.

FIG. 2A is an illustration depicting an example HMD that includes atleast one diffraction type polarizing beam splitter, in accordance withtechniques described in this disclosure.

FIG. 2B is an illustration depicting another example HMD that includesat least one diffraction type polarizing beam splitter, in accordancewith techniques described in this disclosure.

FIG. 3 is a block diagram showing example implementations of a consoleand an HMD of the artificial reality system of FIG. 1, in accordancewith techniques described in this disclosure.

FIG. 4 is a block diagram depicting an example HMD of the artificialreality system of FIG. 1, in accordance with the techniques described inthis disclosure.

FIGS. 5A-5D are illustrations depicting example diffraction typepolarizing beam splitters, in accordance with the techniques describedin this disclosure.

FIG. 6 is an illustration depicting an example diffraction typepolarizing beam splitter and spatial light modulator, in accordance withthe techniques described in this disclosure.

FIGS. 7A-7D are illustrations depicting an example combination of twodiffraction type polarizing beam splitters, in accordance with thetechniques described in this disclosure.

FIG. 8 is an illustration depicting an example display system, inaccordance with the techniques described in this disclosure.

FIG. 9 is an illustration depicting an example display system, inaccordance with the techniques described in this disclosure.

FIG. 10 is an illustration depicting an example display system, inaccordance with the techniques described in this disclosure.

FIG. 11 is an illustration depicting an example display system, inaccordance with the techniques described in this disclosure.

FIG. 12 is an illustration depicting an example display system, inaccordance with the techniques described in this disclosure.

FIG. 13 is an illustration depicting an example light source, inaccordance with the techniques described in this disclosure.

FIG. 14 is an illustration depicting an example display system, inaccordance with the techniques described in this disclosure.

FIG. 15 is an illustration depicting an example eye-tracking system, inaccordance with the techniques described in this disclosure.

FIG. 16 is an illustration depicting an example eye-tracking system, inaccordance with the techniques described in this disclosure.

FIG. 17 is an illustration depicting an example eye-tracking system, inaccordance with the techniques described in this disclosure.

FIG. 18 is an illustration depicting an example eye-tracking system, inaccordance with the techniques described in this disclosure.

FIG. 19 is an illustration depicting an example eye-tracking system, inaccordance with the techniques described in this disclosure.

FIGS. 20A-20B are schematic diagrams illustrating a switchableholographic polymer-dispersed liquid crystal (H-PDLC) grating, inaccordance with the techniques described in this disclosure.

FIGS. 21A-21B are schematic diagrams illustrating an example liquidcrystal surface relief grating (LC-SRG), in accordance with thetechniques described in this disclosure.

FIGS. 22A-22B are schematic diagrams illustrating another exampleLC-SRG, in accordance with the techniques described in this disclosure.

FIGS. 23A-23F are schematic diagrams illustrating examples of a PBPgrating 2400, a reflective PVG (r-PVG) 2430, and a transmissive PVG(t-PVG) 2460, in accordance with the techniques described in thisdisclosure.

FIGS. 24A-24B are schematic diagrams illustrating an example liquidcrystal shutter in combination with a passive diffraction grating, inaccordance with the techniques described in this disclosure.

FIGS. 25A-25B are schematic diagrams illustrating another example liquidcrystal shutter in combination with a passive diffraction grating, inaccordance with the techniques described in this disclosure.

FIGS. 26A-26B are schematic diagrams illustrating another example liquidcrystal shutter in combination with a passive diffraction grating, inaccordance with the techniques described in this disclosure.

DETAILED DESCRIPTION

In typical LCoS imaging applications, an illumination source is directedtowards the LCoS display through a conventional polarizing beam splitter(PBS). The PBS passes or directs light of a polarization, for examplelinear polarization, towards the LCoS display. The LCoS display encodesimage information via spatial modulation of the phase, and therefore thepolarization, of the incident light, and reflects the light back to thePBS. The PBS directs a portion of the reflected light, based onpolarization, towards a projection system for projection of the imageinformation to an image plane. Often, the conventional PBS is heavy andconstrains the mechanical design, e.g., the form factor, of the LCoSillumination system.

The present disclosure is directed to optical assemblies configured topolarize and direct light. The optical assemblies may be used in, forexample, an artificial reality, mixed reality, virtual reality, oraugmented reality system utilizing an LCoS projector, an eye trackingsystem, or the like. For instance, the optical assembly may be used topolarize and direct light to an LCoS display and then additionallyreceive polarized light reflected from the LCoS display and direct it toa projection system. The optical assembly may include two or moredirectors of light, whose function is to redirect at least portion ofincident light. The light directors may include conventional opticalelements such as mirrors, prisms, etc. In the present disclosure, atleast one light director may be a DT-PBS that is configured to splitlight into two orthogonal polarization states (linear or circular),redirect a first polarization state in a first direction while directinga second polarization state in a different direction or withoutredirecting the second polarization state. The DT-PBS may includerelatively thin, light-weight optical elements, such as transmissive andreflective PVG, a liquid crystal filled surface relief grating (LC SRG),a holographic polymer dispersed liquid crystal gratings (PDLC), a PBPgrating or any other optic that can selectively transmit onepolarization while directing a second polarization state in a differentdirection or without redirecting the second polarization state. DT-PBS'shave the advantage of being thin and lightweight, allowing LCoS systemto have a small form factors not possible using conventional optic. Inaddition, DT-PBS can be designed in pairs to at least partiallycompensate for dispersion.

In other examples, the present disclosure is also directed to an opticalassembly for directing light to an eye tracking detector afterreflecting off an eye. DT-PBS's, because they are thin, lightweight, andcan compensate for dispersion, enable alternative form factors and theuse of broadband illumination for eye tracking, e.g., LEDs. In someexamples, broadband illumination may include light comprising a range ofwavelengths, for example, a 100 nm range of wavelengths, a 500 nm rangeof wavelengths, the range of visible wavelengths, the range ofnear-infrared, mid-infrared, or far-infrared wavelengths, or anycombination thereof. In some examples, narrowband illumination, e.g.from a narrowband light source, may include light comprising a range ofwavelengths, for example, a 1 nm range of wavelengths, a 5 nm range ofwavelengths, a 50 nm range of wavelengths, a 100 nm range ofwavelengths, a range of wavelengths less than a broadband range ofwavelengths (e.g. as from a wavelength-filtered broadband light source),or any combination thereof. In some examples, monochromaticillumination, e.g. from a monochromatic light source, may include lightcomprising a small range of wavelengths, for example, less than a nmrange of wavelengths, or the like. Monochromatic illumination mayinclude illumination from, for example, a laser, a gas discharge lightsource, a mercury lamp, or any narrowband or broadband light source withenough wavelength filtering to reduce the range of wavelengths includedin the illumination.

In some examples, the DT-PBS's can redirect the first polarization statein transmission, e.g., into diffraction grating orders. In otherexamples, the DT-PBS can redirect the first polarization state inreflection, e.g., redirect the light to exit the polarization sensitivelight director through the same surface as which it was incident on thepolarization sensitive light director, e.g., into diffraction gratingorders in reflection.

In some examples, the first polarization state is orthogonal to thesecond polarization state. For example, the DT-PBS can splitnon-polarized light in two orthogonal linear polarizations and redirectone linear polarization at a first angle and transmit the orthogonallinear polarization, e.g., the linear polarization state rotated 90°with respect to the first linear polarization state. By way of anotherexample, the DT-PBS can split non-polarized light in two orthogonalcircular polarizations and redirect right-handed circular polarization(RCP) and transmit left-handed circular polarization (LCP), and viceversa.

FIG. 1 is an illustration depicting an example artificial reality systemthat includes at least one polarization sensitive light director, inaccordance with the techniques described in this disclosure. In theexample of FIG. 1, artificial reality system 100 includes HMD 112, oneor more controllers 114A and 114B (collectively, “controller(s) 114”),and may in some examples include one or more external sensors 90 and/ora console 106. In some examples, artificial reality system 100 may beany of an artificial reality system, an augmented reality system, amixed reality system, and/or a virtual reality system.

HMD 112 is typically worn by user 110 and includes an electronic displayand optical assembly for presenting artificial reality content 122 touser 110. In addition, HMD 112 includes one or more sensors (e.g.,accelerometers) for tracking motion of the HMD 112 and may include oneor more image capture devices 138 (e.g., cameras, line scanners) forcapturing image data of the surrounding physical environment. Althoughillustrated as a head-mounted display, AR system 100 may alternatively,or additionally, include glasses or other display devices for presentingartificial reality content 122 to user 110.

Each controller(s) 114 is an input device that user 110 may use toprovide input to console 106, HMD 112, or another component ofartificial reality system 100. Controller 114 may include one or morepresence-sensitive surfaces for detecting user inputs by detecting apresence of one or more objects (e.g., fingers, stylus) touching orhovering over locations of the presence-sensitive surface. In someexamples, controller(s) 114 may include an output display, which may bea presence-sensitive display. In some examples, controller(s) 114 may bea smartphone, tablet computer, personal data assistant (PDA), or otherhand-held device. In some examples, controller(s) 114 may be asmartwatch, smartring, or other wearable device. Controller(s) 114 mayalso be part of a kiosk or other stationary or mobile system.Alternatively, or additionally, controller(s) 114 may include other userinput mechanisms, such as one or more buttons, triggers, joysticks,D-pads, or the like, to enable a user to interact with and/or controlaspects of the artificial reality content 122 presented to user 110 byartificial reality system 100.

In this example, console 106 is shown as a single computing device, suchas a gaming console, workstation, a desktop computer, or a laptop. Inother examples, console 106 may be distributed across a plurality ofcomputing devices, such as distributed computing network, a data center,or cloud computing system. Console 106, HMD 112, and sensors 90 may, asshown in this example, be communicatively coupled via network 104, whichmay be a wired or wireless network, such as Wi-Fi, a mesh network or ashort-range wireless communication medium, or combination thereofAlthough HMD 112 is shown in this example as being in communicationwith, e.g., tethered to or in wireless communication with, console 106,in some implementations HMD 112 operates as a stand-alone, mobileartificial reality system, and artificial reality system 100 may omitconsole 106.

In general, artificial reality system 100 renders artificial realitycontent 122 for display to user 110 at HMD 112. In the example of FIG.1, a user 110 views the artificial reality content 122 constructed andrendered by an artificial reality application executing on HMD 112and/or console 106. In some examples, the artificial reality content 122may be fully artificial, i.e., images not related to the environment inwhich user 110 is located. In some examples, artificial reality content122 may comprise a mixture of real-world imagery (e.g., a hand of user110, controller(s) 114, other environmental objects near user 110) andvirtual objects 120 to produce mixed reality and/or augmented reality.In some examples, virtual content items may be mapped (e.g., pinned,locked, placed) to a particular position within artificial realitycontent 122, e.g., relative to real-world imagery. A position for avirtual content item may be fixed, as relative to one of a wall or theearth, for instance. A position for a virtual content item may bevariable, as relative to controller(s) 114 or a user, for instance. Insome examples, the particular position of a virtual content item withinartificial reality content 122 is associated with a position within thereal-world, physical environment (e.g., on a surface of a physicalobject).

During operation, the artificial reality application constructsartificial reality content 122 for display to user 110 by tracking andcomputing pose information for a frame of reference, typically a viewingperspective of HMD 112. Using HMD 112 as a frame of reference, and basedon a current field of view as determined by a current estimated pose ofHMD 112, the artificial reality application renders 3D artificialreality content which, in some examples, may be overlaid, at least inpart, upon the real-world, 3D physical environment of user 110. Duringthis process, the artificial reality application uses sensed datareceived from HMD 112, such as movement information and user commands,and, in some examples, data from any external sensors 90, such asexternal cameras, to capture 3D information within the real world,physical environment, such as motion by user 110 and/or feature trackinginformation with respect to user 110. Based on the sensed data, theartificial reality application determines a current pose for the frameof reference of HMD 112 and, in accordance with the current pose,renders the artificial reality content 122.

Artificial reality system 100 may trigger generation and rendering ofvirtual content items based on a current field of view 130 of user 110,as may be determined by real-time gaze tracking of the user, or otherconditions. More specifically, image capture devices 138 of HMD 112capture image data representative of objects in the real-world, physicalenvironment that are within a field of view 130 of image capture devices138. Field of view 130 typically corresponds with the viewingperspective of HMD 112. In some examples, the artificial realityapplication presents artificial reality content 122 comprising mixedreality and/or augmented reality. The artificial reality application mayrender images of real-world objects, such as the portions of aperipheral device, the hand, and/or the arm of the user 110, that arewithin field of view 130 along with virtual objects 120, such as withinartificial reality content 122. In other examples, the artificialreality application may render virtual representations of the portionsof a peripheral device, the hand, and/or the arm of the user 110 thatare within field of view 130 (e.g., render real-world objects as virtualobjects 120) within artificial reality content 122. In either example,user 110 is able to view the portions of their hand, arm, a peripheraldevice and/or any other real-world objects that are within field of view130 within artificial reality content 122. In other examples, theartificial reality application may not render representations of thehand or arm of user 110.

To provide virtual content, the HMD 112 can include an electronicdisplay. In some examples, the display may include a projection display,such as a liquid crystal on silicon (LCoS) projector. In accordance withexamples disclosed herein, the LCoS projector may include a lightsource, at least one DT-PBS, an LCoS display, and projection optics toproject an image positioned at least partially within the field of view130. The at least one DT-PBS may be used as a compact and lightweightsystem component to direct light of some polarization from the lightsource to the LCoS display, e.g. the at least one DT-PBS may be lighterand thinner than current LCoS light directors such as conventionalpolarizing beam splitter cubes (PBS). For example, a conventional PBScube used in a conventional LCoS projector redirects a portion ofincident light having a first linear polarization in a perpendiculardirection with respect to the direction of the light from the lightsource via the polarizing interface of the PBS, which is set at an angleof 45° with respect to the direction of the light from the light source.As such, the depth, e.g., thickness, of the PBS is equal to the beamwidth of the light from the light source in order to achieve apolarizing interface at 45°. Typically, in a conventional LCoSprojection system, light from the light source is pre-polarized by aclean-up polarizer to a linear polarization state that is passed by thePBS, e.g., is not redirected at the polarizing interface of the PBS, andreflected back to the PBS by a LCoS display. The LCoS display encodesspatial information in the light, e.g., an image, via phase delaysintroduced by the LC pixels of the display. The bright and dark statesof the image correspond to two linear orthogonal polarizations, whichare special cases of elliptical polarization. The light of first linearpolarization corresponding to “bright” pixels of display is reflected ata 90° angle by the polarizing interface of the PBS towards an opticalcombiner, whereas the light of the orthogonal linear polarizationcorresponding to “dark” pixels passes through the PBS cube withoutreflection and thus does not reach the optical combiner. The light ofother polarization states that appeared after passing other pixels ispartially reflected and transmitted by the PBS for pixels of varying“gray” levels. As such, a conventional LCoS projector utilizing a PBScube uses a “transmit-reflect” configuration.

In accordance with examples disclosed here, the LCoS projector utilizingdiffraction type polarizing splitters can use multiple configurations,allowing for increased flexibility in design and form factor of theprojector. For example, in some examples, the LCoS projector utilizingDT-PBS may have a “reflect-transmit” configuration as illustrated anddescribed below with respect to FIG. 8, a “transmit-transmit”configuration as illustrated and described below with respect to FIG. 9,a “reflect-reflect” configuration as illustrated and described belowwith respect to FIG. 10, and/or a “transmit-reflect” configuration asillustrated and described below with respect to FIG. 11.

FIG. 2A is an illustration depicting an example HMD 112 that includes atleast one polarization sensitive light director, in accordance withtechniques described in this disclosure. HMD 112 of FIG. 2A may be anexample of HMD 112 of FIG. 1. As shown in FIG. 2A, HMD 112 may take theform of glasses. HMD 112 may be part of an artificial reality system,such as artificial reality system 100 of FIG. 1, or may operate as astand-alone, mobile artificial realty system configured to implement thetechniques described herein.

In this example, HMD 112 are glasses comprising a front frame includinga bridge to allow the HMD 112 to rest on a user's nose and temples (or“arms”) that extend over the user's ears to secure HMD 112 to the user.In addition, HMD 112 of FIG. 2A includes one or more windows 203A and203B (collectively, “windows 203”). Windows 203 may be substantiallytransparent allowing a user a view of objects in a real-world scenethrough windows 203. Windows 203 may also be light guides, e.g.waveguides, for light injected into windows 203 by one or moreprojectors 148A and 148B (collectively, “projectors 148”). Windows 203may include one or more couplers 146A and 146B (collectively, “couplers146”) configured to inject light into windows 203 as lightguides.Windows 203 may further include and one or more combiners 205A and 205B(collectively, “combiners 205”) configured to extract light from windows203, e.g., light from projectors 248 coupled into windows 203. Combiners205 may be further configured to subtend the user's 110 field of view ofa real-world scene, such that both light from objects in a real-worldscene may transmit through combiners 205 and be combined with light thatcomprises virtual objects, e.g. extracted from windows 203 fromprojectors 148. In some examples, the known orientation and position ofwindows 203 relative to the front frame of HMD 112 is used as a frame ofreference, also referred to as a local origin, when tracking theposition and orientation of HMD 112 for rendering artificial realitycontent according to a current viewing perspective of HMD 112 and theuser. In some examples, the projectors 148 can provide a stereoscopicdisplay for providing separate images to each eye of the user.

In the example shown, the combiners 205 cover a portion of the windows203, subtending a portion of the field of view viewable by a user 110through the windows 203. In other examples, the combiners 205 can coverother portions of the windows 203, or the entire area of the windows205.

As further shown in FIG. 2A, in this example, HMD 112 further includesone or more motion sensors 206, one or more integrated image capturedevices 138A and 138B (collectively, “image capture devices 138”), aninternal control unit 210, which may include an internal power sourceand one or more printed-circuit boards having one or more processors,memory, and hardware to provide an operating environment for executingprogrammable operations to process sensed data and present artificialreality content on the combiners 205.

To provide virtual content, the HMD 112 can include an electronicdisplay, for example, as a component of projectors 148. In someexamples, the display may include a projection display, such as a liquidcrystal on silicon (LCoS) projector. In accordance with examplesdisclosed herein, the LCoS projector may include a light source, lightdirectors at least one of which is a DT-PBS, an LCoS display, andprojection optics to project an image positioned at least partiallywithin the field of view. The at least one DT-PBS may be used as acompact and lightweight system component to direct light from the lightsource to the LCoS display, e.g. the at least one polarization sensitivelight director may be lighter and thinner than current LCoS lightdirectors such as polarizing beam splitter cubes (PBS).

FIG. 2B is an illustration depicting another example HMD 112, inaccordance with techniques described in this disclosure. HMD 112 may bepart of an artificial reality system, such as artificial reality system100 of FIG. 1, or may operate as a stand-alone, mobile artificial realtysystem configured to implement the techniques described herein.

In this example, HMD 112 includes a front rigid body and a band tosecure HMD 112 to a user. In addition, HMD 112 includes a window 203configured to present artificial reality content to the user via thecombiner 205. In some examples, the known orientation and position ofwindow 203 relative to the front rigid body of HMD 112 is used as aframe of reference, also referred to as a local origin, when trackingthe position and orientation of HMD 112 for rendering artificial realitycontent according to a current viewing perspective of HMD 112 and theuser. In other examples, HMD 112 may take the form of other wearablehead mounted displays, such as glasses or goggles.

To provide virtual content, the HMD 112 can include an electronicdisplay, for example, as a component of projectors 148. In someexamples, the display may include a projection display, such as a liquidcrystal on silicon (LCoS) projector. In accordance with examplesdisclosed herein, the LCoS projector may include a light source, atleast one DT-PBS, an LCoS display, and projection optics to project animage positioned at least partially within the field of view. The atleast one DT-PBS may be used as a compact and lightweight systemcomponent to direct light from the light source to the LCoS display,e.g. the at least one DT-PBS may be lighter and thinner than currentLCoS light directors such as polarizing beam splitter cube (PBS).

FIG. 3 is a block diagram showing example implementations of anartificial reality system that includes console 106 and HMD 112, inaccordance with techniques described in this disclosure. In the exampleof FIG. 3, console 106 performs pose tracking, gesture detection, anduser interface generation and rendering for HMD 112 based on senseddata, such as motion data and image data received from HMD 112 and/orexternal sensors.

In this example, HMD 112 includes one or more processors 302 and memory304 that, in some examples, provide a computer platform for executing anoperating system 305, which may be an embedded, real-time multitaskingoperating system, for instance, or other type of operating system. Inturn, operating system 305 provides a multitasking operating environmentfor executing one or more software components 307, including applicationengine 340. As discussed with respect to the examples of FIGS. 2A and2B, processors 302 are coupled to electronic display 303, motion sensors206, image capture devices 138, and, in some examples, optical system306. In some examples, processors 302 and memory 304 may be separate,discrete components. In other examples, memory 304 may be on-chip memorycollocated with processors 302 within a single integrated circuit.

In some examples, the electronic display 303 may include a projectiondisplay, such as a liquid crystal on silicon (LCoS) projector. Inaccordance with examples disclosed herein, the LCoS projector mayinclude a light source, at least one DT-PBS, an LCoS display, andprojection optics to project an image positioned at least partiallywithin the field of view. The at least one DT-PBS may be used as acompact and lightweight system component to direct light from the lightsource to the LCoS display, e.g. the at least one DT-PBS may be lighterand thinner than current LCoS light directors such as polarizing beamsplitters (PBS).

In general, console 106 is a computing device that processes image andtracking information received from image capture devices 138 to performgesture detection and user interface and/or virtual content generationfor HMD 112. In some examples, console 106 is a single computing device,such as a workstation, a desktop computer, a laptop, or gaming system.In some examples, at least a portion of console 106, such as processors312 and/or memory 314, may be distributed across a cloud computingsystem, a data center, or across a network, such as the Internet,another public or private communications network, for instance,broadband, cellular, Wi-Fi, and/or other types of communication networksfor transmitting data between computing systems, servers, and computingdevices.

In the example of FIG. 3, console 106 includes one or more processors312 and memory 314 that, in some examples, provide a computer platformfor executing an operating system 316, which may be an embedded,real-time multitasking operating system, for instance, or other type ofoperating system. In turn, operating system 316 provides a multitaskingoperating environment for executing one or more software components 317.Processors 312 are coupled to one or more I/O interfaces 315, whichprovides one or more I/O interfaces for communicating with externaldevices, such as a keyboard, game controller(s), display device(s),image capture device(s), HMD(s), peripheral device(s), and the like.Moreover, the one or more I/O interfaces 315 may include one or morewired or wireless network interface controllers (NICs) for communicatingwith a network, such as network 104.

Software applications 317 of console 106 operate to provide an overallartificial reality application. In this example, software applications317 include application engine 320, rendering engine 322, gesturedetector 324, pose tracker 326, and user interface engine 328.

In general, application engine 320 includes functionality to provide andpresent an artificial reality application, e.g., a teleconferenceapplication, a gaming application, a navigation application, aneducational application, training or simulation applications, and thelike. Application engine 320 may include, for example, one or moresoftware packages, software libraries, hardware drivers, and/orApplication Program Interfaces (APIs) for implementing an artificialreality application on console 106. Responsive to control by applicationengine 320, rendering engine 322 generates 3D artificial reality contentfor display to the user by application engine 340 of HMD 112.

Application engine 320 and rendering engine 322 construct the artificialcontent for display to user 110 in accordance with current poseinformation for a frame of reference, typically a viewing perspective ofHMD 112, as determined by pose tracker 326. Based on the current viewingperspective, rendering engine 322 constructs the 3D, artificial realitycontent which may in some cases be overlaid, at least in part, upon thereal-world 3D environment of user 110. During this process, pose tracker326 operates on sensed data received from HMD 112, such as movementinformation and user commands, and, in some examples, data from anyexternal sensors 90 (FIG. 1), such as external cameras, to capture 3Dinformation within the real-world environment, such as motion by user110 and/or feature tracking information with respect to user 110. Basedon the sensed data, pose tracker 326 determines a current pose for theframe of reference of HMD 112 and, in accordance with the current pose,constructs the artificial reality content for communication, via the oneor more I/O interfaces 315, to HMD 112 for display to user 110.

Pose tracker 326 may determine a current pose for HMD 112 and, inaccordance with the current pose, triggers certain functionalityassociated with any rendered virtual content (e.g., places a virtualcontent item onto a virtual surface, manipulates a virtual content item,generates and renders one or more virtual markings, generates andrenders a laser pointer). In some examples, pose tracker 326 detectswhether the HMD 112 is proximate to a physical position corresponding toa virtual surface (e.g., a virtual pinboard), to trigger rendering ofvirtual content.

User interface engine 328 is configured to generate virtual userinterfaces for rendering in an artificial reality environment. Userinterface engine 328 generates a virtual user interface to include oneor more virtual user interface elements 329, such as a virtual drawinginterface, a selectable menu (e.g., drop-down menu), virtual buttons, adirectional pad, a keyboard, or other user-selectable user interfaceelements, glyphs, display elements, content, user interface controls,and so forth.

Console 106 may output this virtual user interface and other artificialreality content, via a communication channel, to HMD 112 for display atHMD 112.

Based on the sensed data from any of the image capture devices 138, orother sensor devices, gesture detector 324 analyzes the tracked motions,configurations, positions, and/or orientations of controllers 114 and/orobjects (e.g., hands, arms, wrists, fingers, palms, thumbs) of the user110 to identify one or more gestures performed by user 110. Morespecifically, gesture detector 324 analyzes objects recognized withinimage data captured by image capture devices 138 of HMD 112 and/orsensors 90 and external cameras 102 to identify controller(s) 114 and/ora hand and/or arm of user 110, and track movements of controller(s) 114,hand, and/or arm relative to HMD 112 to identify gestures performed byuser 110. In some examples, gesture detector 324 may track movement,including changes to position and orientation, of controller(s) 114,hand, digits, and/or arm based on the captured image data, and comparemotion vectors of the objects to one or more entries in gesture library330 to detect a gesture or combination of gestures performed by user110. In some examples, gesture detector 324 may receive user inputsdetected by presence-sensitive surface(s) of controller(s) 114andprocess the user inputs to detect one or more gestures performed by user110 with respect to controller(s) 114.

FIG. 4 is a block diagram depicting an example in which HMD 112 is astandalone artificial reality system, in accordance with the techniquesdescribed in this disclosure. In this example, like FIG. 3, HMD 112includes one or more processors 302 and memory 304 that, in someexamples, provide a computer platform for executing an operating system305, which may be an embedded, real-time multitasking operating system,for instance, or other type of operating system. In turn, operatingsystem 305 provides a multitasking operating environment for executingone or more software components 417. Moreover, processor(s) 302 arecoupled to electronic display(s) 303, varifocal optical system(s) 306,motion sensors 206, and image capture devices 138.

In some examples, the electronic display 303 may include a projectiondisplay, such as a liquid crystal on silicon (LCoS) projector. Inaccordance with examples disclosed herein, the LCoS projector mayinclude a light source, at least one DT-PBS, an LCoS display, andprojection optics to project an image positioned at least partiallywithin the field of view. The at least one DT-PBS may be used as acompact and lightweight system component to direct light from the lightsource to the LCoS display, e.g. the at least one DT-PBS may be lighterand thinner than current LCoS beam splitters such as polarizing beamsplitter cubes.

In the example of FIG. 4, software components 417 operate to provide anoverall artificial reality application. In this example, softwareapplications 417 include application engine 440, rendering engine 422,gesture detector 424, pose tracker 426, and user interface engine 428.In various examples, software components 417 operate similar to thecounterpart components of console 106 of FIG. 3 (e.g., applicationengine 320, rendering engine 322, gesture detector 324, pose tracker326, and user interface engine 328) to construct virtual user interfacesoverlaid on, or as part of, the artificial content for display to user110.

Similar to the examples described with respect to FIG. 3, based on thesensed data from any of the image capture devices 138 or 102,controller(s) 114, or other sensor devices, gesture detector 424analyzes the tracked motions, configurations, positions, and/ororientations of controller(s) 114 and/or objects (e.g., hands, arms,wrists, fingers, palms, thumbs) of the user to identify one or moregestures performed by user 110.

In examples describe herein, an optical assembly includes DT-PBS that isconfigured to redirect a first polarization state while directing asecond polarization state in a different direction or withoutredirecting the second polarization state. Optical assemblies utilizingDT-PBS may be used in, for example, an HMD of an artificial realitysystems such as HMD 112 of artificial reality system 100. A DT-PBS maypolarize and redirect or leave light undirected in several ways,depending on the configuration of the optical assembly.

FIGS. 5A-5D are illustrations depicting examples of DT-PBS 502, inaccordance with the techniques described in this disclosure. In theexamples shown, each of FIGS. 5A-5C illustrate polarization sensitiveredirection of light by a DT-PBS 502.

FIG. 5A is an illustration depicting an example DT-PBS 502, inaccordance with the techniques described in this disclosure. In theexample shown, DT-PBS 502 may be combined with reflector 503, forexample, reflector 503 may be a mirror or a cholesteric mirror. In theexample shown, unpolarized light 504, e.g. non-polarized or randomlypolarized light 504, is incident on a first surface of DT-PBS 502.DT-PBS 502 transmits a first polarization of light 506 withoutredirection. The transmitted first polarization of light 506 thenreflects from reflector 503 without redirection, for example, firstpolarization of light 506 is reflected such that the reflected angle isof the same magnitude as the incidence angle with respect to the surfacenormal of reflector 503 (e.g., angle “i” equals angle “r”). In theexample shown, randomly polarized light 504 is normally incident, andlight having the first polarization, e.g., first polarization of light506, is reflected normally from reflector 503 in the opposite directionof randomly polarized light 504. DT-PBS 502 reflects a secondpolarization of light 508 with redirection, for example, secondpolarization of light 508 is reflected such that the reflected angle isof different magnitude as the incidence angle with respect to thesurface normal of polarization sensitive light director 502 (e.g. angle“i” does not equal angle “r”). In other words, DT-PBS 502 in combinationwith reflector 503 may be a reflective polarization sensitivediffraction grating that reflects a first polarization withoutdiffraction and both reflects and deflects a second polarization oflight. In some examples, reflector 503 may be a mirror. For example, forlinear first polarization of light 506, reflector 503 may be a mirrorand not change the polarization of first polarization of light 506,e.g., via a phase change upon reflection. In some examples, reflector503 may be a cholesteric mirror. For example, for circular firstpolarization of light 506, reflector 503 may be a cholesteric mirrorconfigured to preserve the polarization of first polarization of light506 after reflection, e.g., to preserve right-handed circular incidentfirst polarization of light 506 as right-handed circular firstpolarization of light 506 after reflection, or to preserve right-handedcircular incident first polarization of light 506 as right-handedcircular first polarization of light 506 after reflection. Reflector 503as a cholesteric mirror may preserve polarization, for example, bycompensating for a phase change of incident first polarization of light506 upon reflection.

In some examples, polarization sensitive light director 502 may be athin, light-weight optical elements such as a PVG, a liquid crystalfilled surface relief grating (LC SRG), a holographic polymer dispersedliquid crystal gratings (PDLC), a PBP grating, or any other optic thatcan selectively transmit one polarization while directing a secondpolarization state in a different direction or without redirecting thesecond polarization state.

FIG. 5B is an illustration depicting an example DT-PBS 502, inaccordance with the techniques described in this disclosure. In theexample shown, unpolarized light 504, e.g. non-polarized or randomlypolarized light 504, is incident on a first surface of DT-PBS 502.DT-PBS 502 splits light in two orthogonal polarizations. A firstpolarization of light 506 is transmitted without redirection, while asecond polarization of light 508 is reflected with redirection. In otherwords, DT-PBS 502 may act as a reflective diffraction grating for asecond polarization of light. In some examples, DT-PBS 502 may transmitand redirect a portion of the second polarization of light in additionto reflecting and redirecting the second polarization of light.

FIG. 5C is an illustration depicting an example DT-PBS 502, inaccordance with the techniques described in this disclosure. In theexample shown, unpolarized light 504, e.g. non-polarized or randomlypolarized light 504, is incident on a first surface of DT-PBS 502.DT-PBS 502 splits light in two orthogonal polarizations. DT-PBS 502transmits a first polarization of light 506 without redirection andtransmits a second polarization of light 508 with redirection, e.g.,DT-PBS 502 may act as a polarization sensitive diffraction grating thattransmits a first polarization without diffraction and both transmitsand diffracts a second polarization of light. In some examples, DT-PBS502 may reflect and redirect the second polarization of light inaddition to transmitting and redirecting the second polarization oflight.

FIG. 5D is an illustration depicting an example DT-PBS 502, inaccordance with the techniques described in this disclosure. In theexample shown, unpolarized light 504, e.g., non-polarized or randomlypolarized light 504, is incident on a first surface of DT-PBS 502.DT-PBS 502 splits light in two orthogonal polarizations. It transmits afirst polarization of light 506 with redirection in a first directionand transmits a second polarization of light 508 with redirection in asecond direction, e.g., DT-PBS 502 may act as a polarization sensitivediffraction grating that transmits and diffracts orthogonalpolarizations in different directions.

In some examples, DT-PBS 502 may be sensitive to linear or circularpolarization. For example, DT-PBS 502 may redirect light of a firstpolarization and not redirect light of a second polarization that isorthogonal to the first polarization.

In some examples, DT-PBS 502 may be sensitive to linear polarization.For example, DT-PBS 502 may be a transmissive or reflective holographicpolymer dispersed liquid crystal grating (H-PDLC), such as illustratedand described below with respect to FIGS. 20A-20B. In some examples,DT-PBS 502 may be a liquid crystal filled surface relief grating(LC-SRG), such as illustrated and described below with respect to FIGS.21A-21B and FIGS. 22A-22B.

In some examples, DT-PBS 502 may be sensitive to circular polarization,for example as a PBP, such as described below with respect to FIGS.23A-23B. In some examples, polarization sensitive light director 502 maybe a reflective or transmissive PVG, such as illustrated and describedbelow with respect to FIGS. 23C-23F.

In some examples, DT-PBS 502 may be a liquid crystal shutter incombination with a passive diffraction grating, such as described belowwith respect to FIGS. 24-26.

In examples provided herein, an optical assembly utilizing DT-PBS may beused in an HMD of an artificial reality system and may include adisplay, for example, a LCoS display. In some examples, the LCoS displaymay function as a spatial light modulator that encodes information inthe form of phase and polarization modulation in the incident lightdirected to the display by a DT-PBS and reflects the spatially modulatedlight back to the DT-PBS. The latter works as polarizer and transformsspatial modulation of polarization to spatial modulation of amplitude,e.g., an image. In some examples, one or more DT-PBS may replace aconventional PBS in an LCoS projection display system and redirect thespatially modulated light to projection optics in order to display theimage encoded by the spatial light modulator.

FIG. 6 is an illustration depicting the working principle of an exampleLCoS display 612 with an example DT-PBS 502. In the example shown, lightof a first polarization 506, is incident on a first surface of DT-PBS502. DT-PBS 502 transmits the first polarization of light 506 withoutredirection. The transmitted light having a first polarization 506 maythen transmit through spatial light modulator 612, reflect from mirror614, and transmit once again through spatial light modulator 614 in theopposite direction. The light may have a phase change imparted to it viathe spatial light modulator. Accordingly, the polarization state of thelight may change after transmission through spatial light modulator 612and reflection from mirror 614. For example, light 604 in the regionbetween the DT-PBS 502 and spatial light modulator 612 may havecomponents of both the first and second polarization states. In theexamples shown, light having the second polarization state 508 may bereflected and redirected by DT-PBS 502, for example, as illustrated anddescribed above with respect to FIG. 5B. In some embodiments, lighthaving the second polarization state 508 may be redirected by DT-PBS 502via diffraction, e.g., light having the second polarization state 508may be reflected and diffracted. In the example shown, light having thefirst polarization 606 exiting spatial light modulator 612 may betransmitted through DT-PBS 502 without redirection. In some examples,light having the first polarization 606 may be spatially modulated inamplitude, phase, and/or polarization state via spatial light modulator612.

In some examples, the spatial light modulator 612 may comprise abirefringent material. The birefringent material may have differentoptical thicknesses at different spatial positions in the plane ofspatial light modulator 612 that is perpendicular to the surface normalof spatial light modulator 612. Additionally, the birefringent materialof spatial light modulator 612 may have a different optical path lengthfor each of the orthogonal components of polarization, e.g., the firstpolarization state and the second polarization state. For example, theindex of refraction for the first polarization state of light, n₁ may bedifferent from the index of refraction for the second polarizationcomponent of light, n₂. The difference between the indices ofrefraction, Δn, for the orthogonal first and second polarization statesis proportional to the phase delay induced by spatial light modulator612 between the two components of light with orthogonal polarization.For example, the phase delay between the two orthogonal polarizationcomponents of light after having propagated through spatial lightmodulator 612, reflected from mirror 614, and propagated back throughspatial light modulator 612 at a particular spatial position isΔϕ=2*(2π-66 nd/λ), where d is the thickness of spatial light modulator612 at that position, λ is the wavelength of the light, the multiplier“2” is because the light propagates through spatial light modulator 612twice. By inducing a phase delay between the two components of theincident polarized light, the polarization state of the light may bechanged. Because the phase delay depends on the thickness of thematerial, the wavelength of the light, and birefringence (e.g. Δn) ofthe material, either one of or both of the thickness and birefringencemay be selected based on the wavelength of light to impart a selectedphase delay, for example, to impart a selected change to thepolarization state of the light at that particular position of thespatial light modulator 612. As such, the spatial light modulator 612may control the magnitude of each of the two orthogonal polarizationstate components exiting spatial light modulator 612, for example, thelight 604.

In some examples, spatial light modulator 612 may comprise a liquidcrystal display, which may change Δn at each pixel (e.g. spatialposition) depending upon an applied voltage, e.g., each pixel of spatiallight modulator 612 may be tunable. DT-PBS 502 may function as bothpolarizer (by passing the first polarization state component andreflecting and redirecting the second) and analyzer (again, by passingthe first polarization state component and reflecting and redirectingthe second). Spatial light modulator 612 and mirror 614 may be combinedin a device, for example, as a LCoS display. In other examples, spatiallight modulator 612 may comprise an anisotropic film.

In examples provided herein, an optical assembly utilizing a pair ofDT-PBS may compensate for dispersion. For example, the redirection ofincident light by diffraction may depend on the wavelength of theincident light. Redirection by more than one DT-PBS enables compensationfor dispersion by adding the opposite dispersion.

FIGS. 7A-7D are illustrations depicting optical assemblies based oncombinations of DT-PBS 502, in accordance with the techniques describedin this disclosure. In the examples shown, the optical assemblies mayextract and displace and/or redirect one polarization component of lightand at least partially compensate for dispersion of the extracted light.In the examples shown, each of FIGS. 7A-7D illustrate respectivecombinations of two DT-PBS 502 configured to compensate for dispersionresulting from each individual DT-PBS 502. In some examples, acombination of two DT-PBS 502 may allow the use of light sources havingbroader emission spectra.

FIG. 7A is an illustration depicting an example combination of twoDT-PBS 502 retaining the incident light propagation direction, inaccordance with the techniques described in this disclosure. In theexample shown, broadband light 704 is incident on a first surface of afirst DT-PBS 502A. DT-PBS 502A transmits and redirects the light 704with dispersion, resulting in a wavelength-dependent angular spread ofthe light. In the examples shown, first DT-PBS 502A disperses the lightinto light 706A having a maximum wavelength included in the light 704that is redirected at a maximum angle, light 706C having a minimumwavelength included in the light 704 that is redirected at a minimumangle, and light 706B having a middle wavelength included in the light704 that is redirected at a middle angle. The spectra of light 706 isthen incident on a DT-PBS 502B. DT-PBS 502B transmits and redirects thelight 706 with substantially equal and opposite dispersion as comparedwith DT-PBS 502A. For example, second DT-PBS 502B redirects the light706A having a maximum wavelength at a maximum angle, light 706C having aminimum wavelength at a minimum angle, and light 706B having a middlewavelength at a middle angle, such that each of light 706A-C areredirected substantially parallel to with respect to each other andparallel to incoming beam 704, as illustrated as broadband light 708. Inother words, this assembly provides displacement of incoming beam 704without changing its direction of propagation. This case, for example,can be realized by using two appropriate gratings with similarproperties; two transmissive PVGs operating with circularly polarizedlight or two LC SRG or two H-PDLC operating with linearly polarizedlight.

FIG. 7B is an illustration depicting an example combination of twoDT-PBS 502 reversing the incident light propagation direction, inaccordance with the techniques described in this disclosure. In theexample shown, broadband light 704 is incident on a first surface of afirst DT-PBS 502A. The DT-PBS 502A reflects and redirects the light 704with dispersion, resulting in a wavelength-dependent angular spread ofthe light. In the examples shown, first DT-PBS 502A disperses the lightinto light 706A having a maximum wavelength included in the light 704that is redirected at a maximum angle, light 706C having a minimumwavelength included in the light 704 that is redirected at a minimumangle, and light 706B having a middle wavelength included in the light704 that is redirected at a middle angle. The dispersed light 706 isthen incident on a second DT-PBS 502B. The DT-PBS 502B transmits andredirects all spectral components of the dispersed light 706 in thedirection opposite to the initial direction of light 704 at the entranceto the DT-PBS assembly. To achieve this, second DT-PBS 502B redirectsthe light 706A having a maximum wavelength at a maximum angle, light706C having a minimum wavelength at a minimum angle, and light 706Bhaving a middle wavelength at a middle angle, such that each of light706A-C are redirected substantially parallel to with respect to eachother, as illustrated as broadband light 708. Thus, this assemblyprovides displacement of incoming beam 704 and changes its propagationdirection to the opposite.

FIG. 7C is an illustration depicting an example combination of twoDT-PBS 502 retaining the incident light propagation direction, inaccordance with the techniques described in this disclosure. In theexample shown, broadband light 704 is incident on a first surface of aretaining 502A. DT-PBS 502A reflects and redirects the light 704 withdispersion, resulting in a wavelength-dependent angular spread of thelight. In the examples shown, first DT-PBS 502A disperses the light intolight 706A having a maximum wavelength included in the light 704 that isredirected at a maximum angle, light 706C having a minimum wavelengthincluded in the light 704 that is redirected at a minimum angle, andlight 706B having a middle wavelength included in the light 704 that isredirected at a middle angle. The dispersed light 706 is then incidenton a second DT-PBS 502B. The DT-PBS 502B reflects and redirects thelight 706 with substantially the same magnitude of dispersion. Forexample, second polarization sensitive light director 502B redirects thelight 706A having a maximum wavelength at a maximum angle, light 706Chaving a minimum wavelength at a minimum angle, and light 706B having amiddle wavelength at a middle angle, such that each of light 706A-C areredirected substantially parallel to with respect to each other, so thatall spectral components are parallel and combined in one beamillustrated as broadband light 708.

FIG. 7D is an illustration depicting an example combination of twoDT-PBS 502 displacing and reversing the incident light propagationdirection, in accordance with the techniques described in thisdisclosure. In the example shown, broadband light 704 is incident on afirst DT-PBS 502A. The DT-PBS 502A transmits and redirects the light 704with dispersion, resulting in a wavelength-dependent angular spread ofthe light. In the examples shown, first DT-PBS 502A disperses the lightinto light 706A having a maximum wavelength included in the light 704that is redirected at a maximum angle, light 706C having a minimumwavelength included in the light 704 that is redirected at a minimumangle, and light 706B having a middle wavelength included in the light704 that is redirected at a middle angle. The spectra of light 706 isthen incident on a second DT-PBS 502B. The DT-PBS 502B reflects andredirects the light 706 with substantially the same magnitude ofdispersion. For example, second DT-PBS 502B redirects the light 706Ahaving a maximum wavelength at a maximum angle, light 706C having aminimum wavelength at a minimum angle, and light 706B having a middlewavelength at a middle angle, such that each of light 706A-C areredirected substantially parallel to with respect to each other, asillustrated as broadband light 708. Thus, this assembly, same as theassembly shown in FIG. 7B, provides displacement of incoming beam 704and change of its propagation direction to the opposite.

In examples provided herein, an optical assembly utilizing polarizationsensitive light directors may be used in an HMD of an artificial realitysystem, an augmented reality system, a virtual reality system, and/or amixed reality system, and may include a display, for example, a LCoSdisplay, two or more DT-PBS, and a waveguide, for example, window 203 asillustrated and described above with respect to FIGS. 2A and 2B. Ingeneral, optical assemblies utilizing DT-PBS may enable multipleconfigurations, for example, DT-PBS configured as reflect-transmit,transmit-transmit, reflect-reflect, and transmit-reflect, as illustratedand described below with respect to FIGS. 8-11.

FIG. 8 is an illustration depicting an example display system 800, inaccordance with the techniques described in this disclosure. The exampledisplay system 800 includes two DT-PBS 802A and 802B, a light source804, and a display 806, for example, an LCoS display 806. In someexamples, display system 800 may include a polarizer 808, for example, alinear or circular polarizer 808, an optical combiner 810, and awaveguide input coupler 812. In some examples, display system 800 mayinclude projection optics to reimage the image content of display 806with or without magnification (not shown).

In the example shown, light source 804 may be an area light source. Insome examples, light source 804 may include a plurality of smallersources, for example, light emitting diodes or lasers. In some examples,light source 804 may be a point-like light source. In some examples,light from light source 802 may include a broad range of wavelengths(e.g., broadband), may include a narrow band of wavelengths, may bemonochromatic, or may include any combination of broadband, narrowband,and/or monochromatic light sources. In the example shown, light fromlight source 804 may be broadband, unpolarized, and directed towards afirst DT-PBS 802A. In some examples, polarizer 808 is positioned betweenlight source 804 and first DT-PBS 802A and is configured to select afirst polarization, for example, by transmitting (e.g., “passing”) afirst polarization and not transmitting a second polarization orthogonalto the first polarization (e.g., “blocking” or “filtering out” thesecond polarization). Alternatively, the first polarization can beextracted from non-polarized light illuminated from source 804 by DT-PBS802A, e.g., polarizer 808 may be omitted. In some examples, light source804 may be polarized, and polarizer 808 may be omitted.

In the example shown, first DT-PBS 802A may be a reflective DT-PBS. Forexample, light may be both reflected and deflected, e.g. reflected at anangle other than the incident angle with opposite sign as in reflectionvia a mirror. First DT-PBS 802A may be sensitive to circular or linearpolarization, for example, the DT-PBS based on PVG and H-PDLC,respectively. In some examples, first DT-PBS 802A is configured to bothreflect and redirect light of the first polarization transmitted (e.g.,passed) through polarizer 808 towards second polarization sensitivelight director 802B. In some examples, first DT-PBS 802A is configuredto both reflect and redirect light of the first polarization transmitted(e.g., passed) through polarizer 808 towards second polarizationsensitive light director 802B, and additionally to convert the firstpolarization to a second polarization, e.g. a second polarizationorthogonal to the first polarization.

In the example shown, second DT-PBS 802B is positioned in the light pathsubstantially between first DT-PBS 802A and display 806. In the examplesshown, second DT-PBS 802B transmits and redirects incident light towardsdisplay 808. In the example shown, second DT-PBS 802B may be atransmissive DT-PBS. For example, light may be both transmitted andredirected, e.g., transmitted at an angle other than the incident angleas in transmission through a window. Second DT-PBS 802B may be anyDT-PBS, for example, any of the DT-PBS discussed above such as a H-PDLC,a PVG, etc. First DT-PBS 802A and second DT-PBS 802B are selected to besensitive to the same type of polarization of light (e.g., bothsensitive to circular polarization or both sensitive to linearpolarization). In some examples, second DT-PBS 802B is configured toboth transmit and redirect light of the first polarization towardsdisplay 808. In some examples, second DT-PBS 802B is configured to bothtransmit and redirect light of the second polarization towards display808. In some examples, second polarization sensitive light director 802Bis additionally configured to convert either of a first or secondpolarization to an orthogonal polarization, e.g., to convert a firstpolarization to a second polarization or to convert a secondpolarization to a first polarization. In general, first polarizationsensitive light director 802A and second polarization light director802B are configured to work in conjunction to redirect light of theappropriate polarization for display 808.

In the example shown, display 808 may be any type of display, forexample, an LCoS display 808. The display 808 may include both areflector, such as a silicon backplane, and a spatial light modulator,such as pixelized LC layer of an LCoS device. Display 808 may modulatethe phase and/or amplitude of incident light. The phase and polarizationof the light exiting the display 808 may be spatially modulated owing toelectrically set LC orientation in each pixel. This light passingthrough the DT-PBS 802B, e.g., in the opposite direction and fromdisplay 808, is split in two orthogonal polarizations by DT-PBS 802B andonly one polarization is transmitted, e.g., directed, towards a target,e.g., optical combiner 810, such as a waveguide. The amplitude of thislight is spatially modulated and as such contains image informationperceived by a viewer's eye. In other words, DT-PBS 802B mayadditionally convert a spatial modulation of polarization light fromdisplay 808 to a spatial modulation of amplitude of light. In someexamples, DT-PBS 802A and DT-PBS 802B direct, redirect, or are sensitiveto the same type of polarization, e.g., circular or linear polarization.In some examples, DT-PBS 802A and DT-PBS 802B may have substantially thesame grating period and may be configured to compensate for dispersion.

In the example shown, the spatially modulated light may then be incidenton a waveguide input coupler 812, coupling the spatially modulated lightinto waveguide 810 for transport and output coupling at a desiredlocation.

In general, the example display system 800 includes a reflective DT-PBS802A and a transmissive DT-PBS 802B. In some examples, the displaysystem 800 may allow for a more compact optical display system, and/or adisplay system having an alternative form factor that eases and/orimproves packaging of the optical display system.

FIG. 9 is an illustration depicting an example display system 900, inaccordance with the techniques described in this disclosure. The exampledisplay system 900 includes two DT-PBS 902A and 902B, a light source804, and a display 806, for example, an LCoS display 806. In someexamples, display system 900 may include a polarizer 808, for example, alinear or circular polarizer 808, an optical combiner 810, and awaveguide input coupler 812. In some examples, display system 900 mayinclude projection optics to reimage the image content of display 806with or without magnification (not shown). The example display system900 includes two transmissive DT-PBS 902A and 902B. DT-PBS 902A and 902Bare sensitive to the same kind of polarization (linear or circular). Insome examples, the display system 900 may allow for a more compactoptical display system, and/or a display system having an alternativeform factor that eases and/or improves packaging of the optical displaysystem.

In the example shown, light source 804, display 806, and polarizer 808may be similar to or substantially the same as light source 804, display806, and polarizer 808 illustrated and described above with reference toFIG. 8. Additionally, in some implementations, polarizer 808 may beomitted, as described with reference to FIG. 8.

In the example shown, first DT-PBS 902A may be a transmissive DT-PBS,such as described above with respect to DT-PBS 802B of FIG. 8. In theexample shown, first DT-PBS 902A is configured to both transmit andredirect light of the selected polarization towards second DT-PBS 902B.In some examples, first DT-PBS 902A may additionally be configured toconvert the selected polarization state to a different polarizationstate, e.g. the orthogonal polarization state.

In the example shown, second DT-PBS 902B is positioned in the light pathsubstantially between first DT-PBS 902A and display 806 and may be atransmissive DT-PBS. Second DT-PBS 902B is configured to both transmitand redirect light of the appropriate polarization towards display 808as described above with respect to FIG. 8.

In the example shown, the light reflected from LCoS with spatiallymodulated phase and/or polarization, may enter the second DT-PBS 902Bagain. In this case, the second DT-PBS 902B splits the incident light intwo orthogonal polarizations: the earlier preselected polarizationcomponent with spatially modulated amplitude is transmitted and directedtowards a target, e.g., optical combiner 810, such as a waveguide,whereas the light of additional (orthogonal) polarization is redirectedin a different direction. In other words, DT-PBS 902B may additionallyconvert a spatial modulation of polarization light from display 808 to aspatial modulation of amplitude of light. In some examples, DT-PBS 902Aand DT-PBS 902B direct, redirect, or are sensitive to the same type ofpolarization, e.g., circular or linear polarization. In some examples,DT-PBS 902A and DT-PBS 902B may have substantially the same gratingperiod and may be configured to compensate for dispersion.

FIG. 10 is an illustration depicting an example display system 1000, inaccordance with the techniques described in this disclosure. The exampledisplay system 1000 includes two DT-PBS 1002A and 1002B, a light source804, and a display 806, for example, an LCoS display 806. In someexamples, display system 1000 may include a polarizer 808, for example,a linear or circular polarizer 808, an optical combiner 810, and awaveguide input coupler 812. As described above, in some instances,polarizer 808 may be omitted. In some examples, display system 1000 mayinclude projection optics to reimage the image content of display 806with or without magnification (not shown). The example display system1000 includes two reflective DT-PBS 1002A and 1002B. In some examples,the display system 1000 may allow for a more compact optical displaysystem, and/or a display system having an alternative form factor thateases and/or improves packaging of the optical display system.

In the example shown, light source 804, display 806, and polarizer 808may be similar to or substantially the same as light source 804, display806, and polarizer 808 illustrated and described above with reference toFIG. 8.

In the example shown, first DT-PBS 1002A may be a reflectivepolarization sensitive light director, such as described above withrespect to FIG. 8. In the example shown, first DT-PBS 1002A isconfigured to both reflect and redirect light of the selectedpolarization towards second DT-PBS 1002B. In some examples, first DT-PBS1002A may additionally be configured to convert the selectedpolarization state to a different polarization state, e.g. theorthogonal polarization state.

In the example shown, second polarization sensitive light director 1002Bis positioned in the light path substantially between first polarizationsensitive light director 1002A and display 806, and may be a reflectiveDT-PBS, such as described above with respect to FIG. 8. Second DT-PBS1002B is configured to both transmit and redirect light of theappropriate polarization towards display 808 as described above withrespect to FIG. 8.

In the example shown, the light reflected from LCoS with spatiallymodulated phase and/or polarization, may be incident on the secondDT-PBS 1002B again. In this case, the second DT-PBS 1002B splits theincident light in two orthogonal polarizations: the earlier preselectedpolarization component with spatially modulated amplitude is transmittedand directed towards a target, e.g., optical combiner 810, such as awaveguide, whereas the light of additional (orthogonal) polarization isreflected and redirected in a different direction. In other words,DT-PBS 1002B may additionally convert a spatial modulation ofpolarization light from display 808 to a spatial modulation of amplitudeof light. In some examples, DT-PBS 1002A and DT-PBS 1002B direct,redirect, or are sensitive to the same type of polarization, e.g.,circular or linear polarization. In some examples, DT-PBS 1002A andDT-PBS 1002B may have substantially the same grating period and may beconfigured to compensate for dispersion.

FIG. 11 is an illustration depicting an example display system 1100, inaccordance with the techniques described in this disclosure. The exampledisplay system 1100 includes two DT-PBS 1102A and 1102B, a light source804, and a display 806, for example, an LCoS display 806. In someexamples, display system 1100 may include a polarizer 808, for example,a linear or circular polarizer 808, an optical combiner 810, and awaveguide input coupler 812. As described above, in some instances,polarizer 808 may be omitted. In some examples, display system 1100 mayinclude projection optics to reimage the image content of display 806with or without magnification (not shown). The example display system1100 includes two reflective DT-PBS 1102A and 1102B. In some examples,the display system 1100 may allow for a more compact optical displaysystem, and/or a display system having an alternative form factor thateases and/or improves packaging of the optical display system.

In the example shown, light source 804, display 806, and polarizer 808may be similar to or substantially the same as light source 804, display806, and polarizer 808 illustrated and described above with reference toFIG. 8.

In the example shown, first polarization sensitive light director 1102Amay be a reflective DT-PBS, such as described above with respect to FIG.8. In the example shown, first DT-PBS 1102A is configured to bothreflect and redirect light of the selected polarization towards secondDT-PBS 1102B. In some examples, first DT-PBS 1102A may additionally beconfigured to convert the selected polarization state to a differentpolarization state, e.g. the orthogonal polarization state.

In the example shown, second DT-PBS 1102B is positioned in the lightpath substantially between first DT-PBS 1102A and display 806, and maybe a reflective DT-PBS, such as described above with respect to DT-PBS802A of FIG. 8. Second DT-PBS 1102B is configured to both reflect andredirect light of the appropriate polarization towards display 808 asdescribed above with respect to DT-PBS 802A of FIG. 8 and DT-PBS 1002Bof FIG. 10.

In the example shown, the light reflected from LCoS with spatiallymodulated phase and/or polarization, may be incident on the secondDT-PBS 1102B again. In this case, the second DT-PBS 1102B splits theincident light in two orthogonal polarizations: the earlier preselectedpolarization component with spatially modulated amplitude is transmittedand directed towards a target, e.g., optical combiner 810, such as awaveguide, whereas the light of additional (orthogonal) polarization isredirected in a different direction. In other words, DT-PBS 1102B mayadditionally convert a spatial modulation of polarization light fromdisplay 808 to a spatial modulation of amplitude of light. In someexamples, DT-PBS 1102A and DT-PBS 1102B direct, redirect, or aresensitive to the same type of polarization, e.g., circular or linearpolarization. In some examples, DT-PBS 1102A and DT-PBS 1102B may havesubstantially the same grating period and may be configured tocompensate for dispersion.

In some examples, optical assemblies utilizing DT-PBS may enableadditional configurations, for example, to efficiently use the lightfrom the light source by using both orthogonal polarization states fordisplay in a left-eye/right-eye configuration. For example, FIG. 12 isan illustration depicting an example display system 1100, in accordancewith the techniques described in this disclosure. The example displaysystem 1100 includes four DT-PBS 1202A-L, 1202B-L, 1202A-R, and 1202B-R,a light source 804, and two displays 806L and 806R, for example, LCoSdisplays 806L and 806R. In some examples, display system 1200 mayinclude a waveguide 810, and a waveguide input coupler 812. In someexamples, display system 1200 may include projection optics to reimagethe image content of display 806 with or without magnification (notshown). The example display system 1200 includes two reflective DT-PBS1202A-L and 1202A-R, and two transmissive DT-PBS 1202B-L and 1202B-R,which may enable projection of virtual content independently to the leftand right eyes of a user, for example, for stereoscopic presentation ofvirtual content. In some examples, the display system 1200 may allow fora more compact optical display system, and/or a display system having analternative form factor that eases and/or improves packaging of theoptical display system. In some examples, display system 1200 may allowfor more efficient use of unpolarized light emitted by source 804, e.g.,by utilizing both polarization states rather than selecting one andfiltering out the other. In some examples, display system 1200 may allowfor the use of a single light source 804 for two displays toindependently display content to a user's left eye and right eye. Insome examples, display system 1200 allow for at least part of theoptical assembly for both the left eye and right eye paths to have acommon optical axis, for example, the light source and at least two ofthe polarization sensitive light directors may be aligned via a commonoptical axis.

In the example shown, light source 804 and displays 806L and 806R may besimilar to or substantially the same as light source 804 and display 806illustrated and described above with reference to FIG. 8.

In the example shown, and in contrast with systems 800-1100, system 1200does not include a polarizer positioned between light source 804 andfirst polarization sensitive light director. Instead, the example insystem 1200 utilizes two pairs of DT-PBS serving as polarizationsensitive light directors, with each pair sensitive to the orthogonalpolarization with respect to the other pair. For example, DT-PBS 1202A-Land 1202B-L may be sensitive to a first polarization, e.g. may redirecta first polarization to a user's left eye, while DT-PBS 1202A-R and1202B-R may be sensitive to a second polarization orthogonal to thefirst polarization, e.g. may redirect a second polarization to a user'sright eye. In some examples, system 1200 may more efficiently use lightas compared to a system utilizing a polarizer in between the lightsource and the first DT-PBS, for example, by using the DT-PBS to bothdirect a first polarization of light for use by the system and passing asecond polarization of light to a second DT-PBS for use by the system.In other words, system 1200 may include DT-PBS to use both polarizationsof light emitted by the light source as compared to selecting onepolarization via an absorbing linear or circular polarizer locatedbetween the light source and the first DT-PBS.

In the example shown, DT-PBS 1202A-R may be a reflective DT-PBS, such asdescribed above with respect to FIG. 8. In the example shown, DT-PBS1202A-R is configured to both reflect and redirect light of a firstpolarization towards second DT-PBS 1202B-R. In some examples, DT-PBS1202A-R may additionally be configured to convert the selectedpolarization state to a different polarization state, e.g. theorthogonal polarization state. Further, DT-PBS 1202A-R is configured totransmit, e.g., “pass,” a second polarization, for example, a secondpolarization orthogonal to the first polarization.

In the example shown, DT-PBS 1202A-L may be a reflective DT-PBS, such asdescribed above with respect to FIG. 8. In the example shown, DT-PBS1202A-L is configured to both reflect and redirect light of a secondpolarization orthogonal to the first polarization reflected andredirected by DT-PBS 1202A-R. In the example shown, DT-PBS 1202A-L isconfigured to reflect and redirect the second polarization towardssecond DT-PBS 1202B-R. In some examples, DT-PBS 1202A-R may additionallybe configured to convert the selected polarization state to a differentpolarization state, e.g. the orthogonal polarization state.

In some examples, any of DT-PBS 1202A-L, 1202B-L, 1202A-R, and 1202B-Rmay convert the polarization of incident light to a differentpolarization state, e.g. the orthogonal polarization state, andtherefore for ease of description, the first polarization reflected andredirected via DT-PBS 1202A-R in the example shown will be referred toas “right-selected” polarization and the polarization orthogonal to theright-selected polarization that is reflected and redirected via DT-PBS1202A-L will be referred to as “left-selected” polarization.

In the example shown, DT-PBS 1202B-R is positioned in the light pathsubstantially between DT-PBS 1202A-R and display 806R, and may be atransmissive DT-PBS, such as described above with respect to FIG. 8.DT-PBS 1202B-R is configured to both transmit and redirectright-selected polarized light towards display 808R.

In the example shown, DT-PBS 1202B-L is positioned in the light pathsubstantially between DT-PBS 1202A-L and display 806L, and may be atransmissive DT-PBS, such as described above with respect to FIG. 8.DT-PBS 1202B-L is configured to both transmit and redirect left-selectedpolarized light towards display 808L.

In the example shown, the left- and right-selected light that hasspatially modulated phase and/or polarization after reflection fromdisplay may be incident on DT-PBS 1202B-L and DT-PBS 1202B-R,respectively, again. After passing through the splitters 1202B-L and1202B-R the light becomes uniformly polarized and the spatial modulationof polarization is transformed to a spatial modulation of amplitude,which may be perceived by eye as an image. This image light may then beincident on waveguide input couplers 812R and 812L, respectively,thereby coupling the image light into waveguides 81OR and 810L,respectively, for transport and output coupling at a desired locationand to the right and left eyes, respectively, of the user.

In some examples, display system 1200 may be of any thereflective-transmissive, transmissive-transmissive,reflective-reflective, and reflective-reflective configurationsdescribed above with respect to FIGS. 8-11. For example, DT-PBS 1202A-L,1202B-L, 1202A-R, and 1202B-R may be reflective or transmissive, and maybe combined in any of the configurations described above with respect toFIGS. 8-11. Further, the left and right sides may be independentlyconfigured, for example, having the same configuration type (e.g.reflective-transmissive) or different configuration types.

In each of FIGS. 8-12, the light source 804 may be a broadband lightsource, e.g. having a plurality of wavelengths of varying amplitude.Each of DT-PBS 802, 902, 1002, 1102, 1202 may be dispersive, e.g.redirect light in a wavelength-dependent angle. Each of display systems800, 900, 1000, 1100, and 1200 include at least two coupled DT-PBS, andmay compensate for dispersion, for example, as described above withrespect to FIGS. 7A-C.

In some examples, optical assemblies utilizing DT-PBS may be configuredto increase the contrast of the final displayed image, increase energyefficiency, realize zonal illumination, or combinations thereof. Forexample, the light source used may be an area source, or an areacomprising a plurality of point-like sources, that can selectivelychange the brightness based on spatial position as described below withrespect to FIG. 13. In some examples, one or more of the DT-PBS may beswitchable based on spatial position, as described below with respect toFIG. 14. In some examples, the contrast of the displayed image may beincreased by locally dimming the light source, or locally selecting thelight to be directed to the display via the polarization sensitive lightdirectors, or any combination of the two.

FIG. 13 is an illustration depicting an example light source 1404, inaccordance with the techniques described in this disclosure. The examplelight source 1404 includes a plurality of individual point-like sources,e.g. smaller area sources, for example, LEDs, organic light emittingdiodes (OLEDs), laser sources, etc. The light source 1404 may be used aslight source 804 in any of the preceding figures, e.g., FIGS. 8-12, andFIG. 14 below.

In the example shown, the plurality of individual light sources may beselectively activated. For example, individual light source 1402 isactivated and emits light, and individual light source 1406 is notactivated and does not emit light. In some examples, selectivelyactivating light sources based on spatial position within light source1304 may improve the contrast of a display system and/or improve theenergy efficiency of a display system, e.g. any of display systems 800,900, 1000, 1100, and 1200. In some examples, selectively activatinglight sources based on spatial position within light source 1304 mayenable and/or improve zone illumination, e.g., illumination of only aportion of the image at a particular time.

FIG. 14 is an illustration depicting an example display system 1500, inaccordance with the techniques described in this disclosure. The exampledisplay system 1500 is substantially similar to system 800 of FIG. 8,aside from differences described herein. In particular, unlike system800, system 1500 includes two DT-PBS 1502A and 1502B, at least one ofwhich may be pixelated.

In the example shown, first pixelated DT-PBS 1502A may be configured tobe switchable, e.g. electronically controllable. For example, firstDT-PBS 1502A may be switched between at least a first state configuredto both reflect and redirect light of the selected polarization and atleast a second state configured to transmit all light withoutredirection.

Additionally, first pixelated DT-PBS 1502A may be pixelated, such thatpixelated DT-PBS 1502A includes a plurality of switchable portions. Forexample, first pixelated DT-PBS 1502A may be spatially divided intodomains by a transparent electrode configuration such that individualdomains are independently switchable. First pixelated DT-PBS 1502A maybe a diffraction element based on an electronically switchablebirefringent material disposed between two substrates, and theindividual domains may be determined by a transparent electrode patternon a surface of one of the substrates of first pixelated DT-PBS 1502A.The other substrate may have an area transparent conductor, or anopposing transparent electrode pattern, disposed on a surface of theopposing substrate, such that a voltage applied to the electrode patternresults in an electric field pattern established between the electrodepattern and the opposing conductor. The birefringent material may alignalong or perpendicularly to the field lines, thereby changing thein-plane birefringence (e.g., Δn) of the material in the local area ofeach domain of the electrode pattern. As such, first pixelated DT-PBS1502A may also function as a spatial modulator to spatially modulateintensity of illumination and to enhance contrast of the display system1500.

In some examples, first pixelated DT-PBS 1502A may be a liquid crystalgrating that is directly driven between one or more states, for example,by an electric field between transparent electrodes. In other examples,first DT-PBS 1502A may be a combination of a passive (e.g.non-switchable) polarization sensitive grating and a switchable halfwaveplate adjacent to it from the side of light incidence. This platelocally changes the polarization of light passing through it toorthogonal, which is not deflected by DT-PBS 1502A to the second DT-PBS1502A and then to display. In other examples, first DT-PBS 1502A may bea combination of a passive (e.g. non-switchable) grating and a pixelatedshutter adjacent to it from the side of light incidence. The examples ofsuitable shutters are pixelated birefringence type, guest-host type andscattering type LC shutters illustrated and described below regarding toFIGS. 24, 25 and 26, respectively. In some examples, configuring firstDT-PBS 1502A to be switchable may enable spatial control of the lightincident on display 806, e.g. spatial amplitude control of the incidentlight, and may result in contrast enhancement of display system 1500 aswell as zone illumination.

In the example shown, second pixelated DT-PBS 1502B is positioned in thelight path substantially between first polarization sensitive lightdirector 1502A and display 806, and may be a transmissive DT-PBS, suchas described above with respect to FIG. 8. Second pixelated DT-PBS 1502Bmay be configured to both transmit and redirect light of the appropriatepolarization towards display 808 as described above with respect to FIG.8. In some examples, second pixelated DT-PBS 1502B may be switchable, asdescribed above with respect to first DT-PBS 1502A.

In the example shown, the spatially modulated light may then be incidenton a waveguide input coupler 812, coupling the spatially modulated lightinto waveguide 810 for transport and output coupling at a desiredlocation.

In the example shown, both first DT-PBS 1502A and second DT-PBS 1502Bare switchable and pixelated. In some examples, either first or secondDT-PBS 1502A and 1502B may be switchable and pixelated, with the otherbeing a passive DT-PBS such as any of DT-PBS 802, 902, 1002, 1102 and/or1202A described above. In addition, first and second DT-PBS 1502A and1502B may be used in any combination or configuration, such as thereflective-transmissive, transmissive-transmissive,transmissive-reflective, reflective-reflective, and/or stereoscopic asdescribed above with respect to FIGS. 8-12.

In some examples, the present disclosure is also directed to an opticalassembly for directing light to an eye tracking detector afterreflecting off an eye. Polarization sensitive light directors, becausethey are thin, lightweight, and can compensate for dispersion, enablesmall form factors and new design solutions, and enable the use ofbroadband illumination for eye tracking, e.g., LEDs. FIGS. 15-19 belowillustrate and describe example optical assemblies for directing lightto an eye-tracking camera, e.g. eye-tracking systems, utilizingpolarization sensitive light directors. FIGS. 15-18 illustrate examplesof light source placement in example eye-tracking systems in areflective-transmissive polarization sensitive light directorconfiguration, and FIGS. 17-19 illustrate reflective-reflective,transmissive-transmissive, and transmissive-reflective combinations ofDT-PBS.

FIG. 15 is an illustration depicting an example eye-tracking system1600, in accordance with the techniques described in this disclosure.The example eye-tracking system 1600 includes two DT-PBS 1602A and1602B, light sources 1604A and 1604B, camera 1606, and eye 1608. In someexamples, the eye-tracking system 1600 may allow for a more compactoptical system, and/or a system having an alternative, e.g., smaller,form factor that eases and/or improves packaging of the eye-trackingsystem. In the example shown, eye-tracking system 1600 includes twoDT-PBS 1602 in a reflective-transmissive configuration. In someexamples, use of at least two DT-PBS 1602 in eye-tracking system 1600may allow for dispersion compensation as described above with respect toFIGS. 7A-C and the use of broadband sources for eye-tracking, forexample, in order to form a clear image of either the sources reflectedby eye 1608 and/or the illuminated eye 1608.

In the example shown, eye-tracking system 1600 includes light sources1604A and 1604B, e.g. “light sources 1604,” collectively. In the exampleshown, light sources 1604 are located near and/or adjacent to a surfaceof DT-PBS 1602A and configured to illuminate eye 1608. In some examples,eye-tracking system 1600 may include only a single light source 1604,and in other examples eye-tracking system 1600 may include three or morelight sources 1608. In some examples, light sources 1604 may be a ringof light sources 1604 configured to illuminate eye 1608 from a pluralityof angles. In some examples, light sources 1604 emit near infrared (NIR)light.

In the example shown, light sources 1604 may be point-like sources, forexample, LEDs, micro-LEDs, lasers, VCSEL laser diodes, etc. In someexamples, light from light sources 1604 may include a broad range ofwavelengths (e.g. broadband), may include a narrow band of wavelengths,may be monochromatic, or may include any combination of broadband,narrowband, and/or monochromatic light sources. In the example shown,light 1620 from light sources 1604 may be broadband and/or unpolarized.

In the example shown, light 1620 from light sources 1604 may reflectfrom eye 1608. In some examples, eye 1608 may be a user's eye, e.g. user110. In some examples, eye 1608 may be a camera, such as an eyeballcamera used in place of user's 110 eye.

In the example shown, reflected light 1630 is incident on first DT-PBS1602A. First polarization sensitive light director 1602A may be areflective DT-PBS. For example, reflected light 1630 may be bothreflected and redirected, e.g. reflected at an angle other than theincident angle with opposite sign as in reflection via a mirror, byfirst DT-PBS 1602 towards second DT-PBS 1602B. First DT-PBS 1602A may beany DT-PBS, for example, any of the DT-PBS discussed above such as aH-PDLC, a PVG, etc. In some examples, first DT-PBS 1602A is configuredto both reflect and redirect light of a first polarization, e.g. aselected polarization. The selected polarization may be linear,circular, or elliptical. In some examples, first DT-PBS 1602A may beconfigured to additionally convert the selected polarization to a secondpolarization, e.g. a second polarization orthogonal to the selectedpolarization.

In the example shown, second DT-PBS 1602B is positioned in the lightpath substantially between first DT-PBS 1602A and camera 1606. In theexamples shown, second DT-PBS 1602B transmits and redirects incidentlight, e.g. reflected light 1630, towards camera 1608. In the exampleshown, second DT-PBS 1602B may be a transmissive polarization sensitivelight director. For example, light may be both transmitted andredirected, e.g. transmitted at an angle other than the incident angleas in transmission through a window. Second DT-PBS 1602B may be anyDT-PBS, for example, any of DT-PBS discussed above such as a H-PDLC, aPVG, etc. In some examples, second DT-PBS 802B is additionallyconfigured to convert either of the first (e.g. selected) or the secondpolarization to an orthogonal polarization, e.g. to convert the selectedpolarization to the second polarization or to convert the secondpolarization to the selected polarization. In general, first DT-PBS1602A and second polarization light director 1602B are configured towork in conjunction to redirect at least a portion of reflected light1630 towards detector 1606.

In some examples, detector 1606 may be any type of camera, for example,a silicon-based CCD array camera, a CMOS array camera, a camera havingan infrared sensitive (e.g. near-infrared, short-infrared, mid-waveinfrared, long-wave infrared sensitive) focal plane array such as amercury cadmium telluride array, an indium antimonide array, an indiumgallium arsenide array, a vanadium oxide array, etc. In another example,detector 1606 may be a position sensitive detector (PSD).

FIG. 16 is an illustration depicting an example eye-tracking system1700, in accordance with the techniques described in this disclosure.The example eye-tracking system 1700 is similar to the eye-trackingsystem 1600 with the location of the light sources 1604 changed to beingnear and/or adjacent to camera 1606 and configured to illuminate eye1608 via reflection and redirection by both DT-PBS 1602A and 1602B. Inthe example shown, light 1620 from light sources 1604 is incident onsecond DT-PBS 1602B, which may transmit and redirect light 1620 of aselected polarization towards first DT-PBS 1602A. First DT-PBS 1602A maythen reflect and redirect the selected polarization of light 1620towards eye 1608, which reflects the light (e.g. reflected light 1630)back towards first DT-PBS 1602A. First and second DT-PBS 1602A and 1602Bthen redirect reflected light 1630 towards detector 1606 as describedabove with respect to FIG. 15. In some examples, light sources 1604 maybe located near and/or adjacent to second DT-PBS 1602B, and in someexamples light sources 1604 may be located anywhere in the optical pathbetween eye 1608 and detector 1606 as illustrated in FIG. 16.

FIG. 17 is an illustration depicting an example eye-tracking system1800, in accordance with the techniques described in this disclosure.The example eye-tracking system 1800 is similar to the eye-trackingsystem 1600 with the location of the light sources 1604 (not shown)being anywhere in the optical path between eye 1608 and detector 1606and configured to illuminate eye 1608. Eye 1608 reflects light fromlight sources 1604, resulting in at least a portion of reflected light1630 being directed towards first DT-PBS 1802A. In the example shown,eye-tracking system 1800 includes two DT-PBS 1802 in areflective-reflective configuration.

In the example shown, first DT-PBS 1802A may be a DT-PBS configured toboth reflect and redirect reflected light 1630 of a selectedpolarization towards DT-PBS 1802B, and may be similar to orsubstantially the same as first DT-PBS 1602A as described above withrespect to FIG. 15.

In the example shown, second DT-PBS 1802B is positioned in the lightpath substantially between DT-PBS 1802A and detector 1606. Second DT-PBS1802B may be configured to both reflect and redirect reflected light1630 towards detector 1608. In the example shown, second DT-PBS 1602Bmay be a reflective DT-PBS, and may be similar to or substantially thesame as first DT-PBS 1602A as described above with respect to FIGS. 15and 16. In some examples, the reflective-reflective configuration ofeye-tracking system 1800 may allow for a different and/or more compacteye-tracking form factor, in addition to dispersion compensation via theuse of two DT-PBS 1802 as described with respect to FIGS. 7A-7C.

FIG. 18 is an illustration depicting an example eye-tracking system1900, in accordance with the techniques described in this disclosure.The example eye-tracking system 1900 is similar to the eye-trackingsystem 1600 with the location of the light sources 1604 (not shown)being anywhere in the optical path between eye 1608 and detector 1606and configured to illuminate eye 1608. Eye 1608 reflects light fromlight sources 1604, resulting in at least a portion of reflected light1630 being directed towards first DT-PBS 1902A. In the example shown,eye-tracking system 1900 includes two DT-PBS 1902 in atransmissive-transmissive configuration.

In the example shown, first DT-PBS 1902A may be a transmissive DT-PBSconfigured to both transmit and redirect reflected light 1630 of aselected polarization towards second DT-PBS 1902B, and may be similar toor substantially the same as second DT-PBS 1602B as described above withrespect to FIG. 15.

In the example shown, second DT-PBS 1902B is positioned in the lightpath substantially between first DT-PBS 1902A and detector 1606. SecondDT-PBS 1902B may be configured to both transmit and redirect reflectedlight 1630 towards detector 1608. In the example shown, second DT-PBS1902B may be similar to or substantially the same as second DT-PBS 1602Bdescribed above with respect to FIG. 15. In some examples, thetransmissive-transmissive configuration of eye-tracking system 1900 mayallow for a different and/or more compact eye-tracking form factor, inaddition to dispersion compensation via the use of two DT-PBS 1902 asdescribe with respect to FIGS. 7A-7C.

FIG. 19 is an illustration depicting an example eye-tracking system2000, in accordance with the techniques described in this disclosure.The example eye-tracking system 2000 is similar to the eye-trackingsystem 1600 with the location of the light sources 1604 (not shown)being anywhere in the optical path between eye 1608 and detector 1606and configured to illuminate eye 1608. Eye 1608 reflects light fromlight sources 1604, resulting in at least a portion of reflected light1630 being directed towards first DT-PBS 2002A. In the example shown,eye-tracking system 2000 includes two DT-PBS 2002 in atransmissive-reflective configuration.

In the example shown, first polarization sensitive light director 2002Amay be a transmissive polarization sensitive light director configuredto both transmit and redirect reflected light 1630 of a selectedpolarization towards second polarization sensitive light director 2002B,and may be similar to or substantially the same as second polarizationsensitive light director 1602B as described above with respect to FIG.15.

In the example shown, second polarization sensitive light director 2002Bis positioned in the light path substantially between first polarizationsensitive light director 2002A and detector 1606. Second DT-PBS 2002Bmay be configured to both reflect and redirect reflected light 1630towards detector 1608. In the example shown, second DT-PBS 2002B may besimilar to or substantially the same as first DT-PBS 1602A as describedabove with respect FIG. 15. In some examples, thetransmissive-reflective configuration of eye-tracking system 2000 mayallow for a different and/or more compact eye-tracking form factor, inaddition to dispersion compensation via the use of two DT-PBS 2002 asdescribed above with respect to FIGS. 7A-7C.

Referring now collectively to FIGS. 15-19, in some examples, either oneor each of DT-PBS 1602, 1702, 1802, 1902 and 2002 may include opticalpower, for example, to converge or diverge light. In some examples,polarization sensitive light directors 1602, 1702, 1802, 1902, and 2002may be curved, and in other examples polarization sensitive lightdirectors 1602, 1702, 1802, 1902, and 2002 may impart a phase delay tothe wavefront of incident light, e.g. light 1520 and/or reflected light1630, so as converge or diverge the light.

In some examples, either one or each of polarization sensitive lightdirectors 1602, 1702, 1802, 1902, and 2002 may be switchable, asdescribed with respect to FIG. 14 above.

In examples provided herein, an optical assembly includes DT-PBS thatare configured to redirect a first polarization state while directing asecond polarization state in a different direction or withoutredirecting the second polarization state. Optical assemblies utilizingDT-PBS may be used in, for example, an HMD of an artificial realitysystems such as HMD 112 of artificial reality system 100. A DT-PBS mayredirect or leave light not redirected in several ways, depending on theconfiguration of the optical assembly. FIGS. 20-26 illustrate exampleDT-PBS and describes examples of polarization sensitive diffractiongratings which may be used as basic elements of a DT-PBS.

FIGS. 20A and 20B are schematic diagrams illustrating a switchableholographic polymer-dispersed liquid crystal (H-PDLC) grating 2102working in the Bragg regime, in accordance with the techniques describedin this disclosure. The examples shown in FIGS. 20A and 20B illustratean example diffraction grating sensitive to linear polarization. FIG.20A illustrates H-PDLC grating 2102 in the on-state, e.g. with a voltageapplied to electrodes of H-PDLC 2102, in which light having either firstlinear polarization 2108 and/or second linear polarization 2110transmits through H-PDLC 2102 without being diffracted or redirected.FIG. 20B illustrates H-PDLC grating 2102 in the off-state in which lighthaving a first linear polarization 2108 is redirected by diffraction byH-PDLC 2102 and light having a second linear polarization 2110 transmitsthrough H-PDLC 2102 without being diffracted or redirected.

In the examples shown in FIGS. 20A and 20B, H-PDLC 2102 includes firstand second substrates including isotropic polymer 2106 and liquidcrystal 2104 disposed between the first and second substrates. H-PDLC2102 may be formed with liquid crystal domains or droplets which may bealigned via holographic recording during phase separation of theisotropic polymer 2106 and liquid crystal 2104. This alignment may bemodified by an external electric or magnetic field applied during phaseseparation. The substrates may include electrodes, or an electrodepattern, to which a voltage may be applied, thereby applying an electricfield between the first and second substrates. The orientation of theliquid crystals may be controlled with the external electric field. Forexample, the orientation of liquid crystal along which the extraordinaryrefractive index of the liquid crystal material of H-PCDL 2102 alignsmay be controlled, e.g., selected, by the application of a voltage tothe electrodes, along with the ordinary refractive index of the liquidcrystal material, which is oriented perpendicular to the extraordinaryrefractive index orientation.

In the examples shown in FIG. 20A, a voltage may be applied to theelectrodes creating an electric field between the electrodes aligningthe liquid crystal 2104 vertically, that is, the director of the liquidcrystal has a major axis that is perpendicular, or substantiallyperpendicular, to the first and second substrates of H-PDLC 2102. Insome examples, H-PDLC 2102 may include any appropriate anisotropicmaterial dispersed in an isotropic matrix.

In the examples shown, the liquid crystal 2104 is aligned substantiallyvertically, that is, the liquid crystal director is perpendicular, orsubstantially perpendicular (e.g., to within 30 degrees from normal), tothe first and second substrates of H-PDLC 2102, e.g., along the z axisas illustrated. In some examples, the ordinary refractive index of theliquid crystal 2104 matches the index of refraction of the polymer 2106.For example, np=no<ne, where no and ne are the ordinary andextraordinary refractive indices of the liquid crystal 2104 and np isthe refractive index of the polymer. Because the liquid crystal isbirefringent, the refractive index of the liquid crystal depends on thepolarization and the propagation direction of light relative to thedirector of the liquid crystal 2104. The propagation of normallyincident light 2108, 2110 is substantially parallel with the director ofthe liquid crystal, and therefore the effective refractive index of theliquid crystal 2104 for the light 2108, 2110 is the ordinary refractiveindex, no, regardless of the polarization of the normally incident light2108, 2110. In the example shown, the polymer index np is substantiallythe same as the ordinary refractive index, no, of the liquid crystal2104, and there is no index difference between the droplets of liquidcrystal 2104 and the polymer 2106. Therefore, the HPDLC 2002 does notdiffract the normally incident light 2108, 2110 and H-PDLC 2102 issubstantially transparent to normally incident light 2108, 2110. As aresult, light 2108, 2110 that is incident to H-PDLC 2102 parallel withthe liquid crystal director, e.g. normally incident in the exampleshown, is transparently transmitted through H-PDLC 2102, e.g.,transmitted with little or no redirection/diffraction.

In the example shown in FIG. 20B, a voltage may be no longer applied tothe electrodes, and the liquid crystal 2104 may align according to thepredetermined preferential direction, as described above. In the exampleshown, the preferential direction of liquid crystal 2104 is alignedsubstantially in-plane, that is, the liquid crystal molecules have adirector that is parallel, or substantially parallel, to the first andsecond substrates of H-PDLC 2102, e.g. in the x-y plane as illustrated.Furthermore, the director may be aligned parallel to the grating vectorof H-PDLC 2102, e.g., preferentially aligned in the x-direction. Becausethe liquid crystal is birefringent, the refractive index of the liquidcrystal depends on the polarization and the propagation direction oflight relative to the director of liquid crystal 2104, e.g. the opticalaxis of liquid crystal 2104. The polarization of normally incident light2110 is substantially perpendicular with the director of liquid crystal2104, e.g., the electrical field of incident light 2110 is perpendicularwith the director of liquid crystal 2104, and therefore the effectiveindex of the liquid crystal 2104 for the light 2110 is the ordinaryrefractive index, no, which substantially matches the polymer indexn_(p). Therefore, the H-PDLC 2102 grating does not diffract the normallyincident light 2110, and H-PDLC 2102 is substantially transparent tonormally incident light 2110. Conversely, the polarization of normallyincident light 2108 is substantially parallel with the director ofliquid crystal 2104, e.g., the electrical field of incident light 2108is parallel with the director of liquid crystal 2104, and therefore theeffective index of the liquid crystal 2104 for the light 2108 is theextraordinary refractive index, ne, which is mismatched with the polymerindex np. Therefore, the liquid crystal 2104 droplets may redirect,e.g., diffract, the normally incident light 2108.

In some examples, the droplets of anisotropic material, e.g., liquidcrystal 2104, may be interconnected within the isotropic material, e.g.,the polymer, as opposed to forming isolated droplets or pores asillustrated in FIGS. 20A and 20B. In some examples, the liquid crystal2104, or anisotropic material, can form a permanent phase in a polymernetwork.

In some examples, H-PDLCs, such as H-PDLC 2102, are sensitive to linearpolarization. In some examples, H-PDLC 2102 may be switchable byswitching the polarization direction of the incident light. In otherexamples, H-PDLC 2102 may be switchable by switching the orientation ofthe liquid crystal 2104 as described above. In some examples, H-PDLC2102 may comprise a Bragg diffraction grating.

FIGS. 21A-21B and FIGS. 22A-22B are schematic diagrams illustratingdifferent example of grating sensitive to linear polarization inaccordance with the techniques described in this disclosure, namely,liquid crystal filled surface relief gratings (LC-SRG) 2200, 2300.

In the example shown in FIGS. 21A and 21B, LC-SRG 2200 includes apassive diffraction grating 2202 and a linear polarization rotator 2204.Passive diffraction grating 2202 may have a surface relief profileformed in a substrate, e.g., via etching, imprinting, etc., and thespaces of the profile may be filled with a birefringent material, forexample, a liquid crystal. In some examples, linear polarization rotator2204 may be a switchable twisted-nematic liquid crystal cell, aswitchable half-wave plate, or any other appropriate linear polarizationrotator.

In the example shown in FIG. 21A, incident light 2208 having a firstlinear polarization transmits through linear polarization rotator 2204,which rotates the polarization of incident light 2208 by 90 degrees suchthat transmitted light 2210 has a second linear polarization that issubstantially perpendicular to the first linear polarization. Thedirector of the liquid crystal material filling the surface reliefpattern spaces may be aligned perpendicularly to the second linearpolarization of light 2210 and may have an ordinary refractive indexthat substantially matches the index of the surface relief profileformed in the substrate of passive diffraction grating 2202. As such,the effective index of refraction for light 2210, because itspolarization is orthogonal to the liquid crystal director, will be theordinary refractive index and the light 2210 will transmit throughpassive diffraction grating 2202 without redirection and/or diffraction,and will exit with the second linear polarization as light 2212.

In the example shown in FIG. 21B, a voltage may be applied to linearpolarization rotator 2204 switching its rotation state as compared withFIG. 21A. For example, incident light 2208 having a first linearpolarization transmits through linear polarization rotator 2204 withoutrotation of its linear polarization such that transmitted light 2214retains the first linear polarization. As such, the effective index ofrefraction for light 2214, because its polarization is parallel to theliquid crystal director, will be the extraordinary refractive index.Because of the index mismatch between the material of the surface reliefprofile formed in the substrate (e.g. or disposed on the substrate),passive diffraction grating 2202 will function as a phase diffractiongrating for light 2214. As such, light 2214 will be redirected, e.g.diffracted, by passive diffraction grating 2202, and will exit with thefirst linear polarization and diffracted based on the phase profileinduced by the index profile of the passive diffraction grating 2202 asdiffracted light 2214.

In some examples, any of the DT-PBS 802-1202, 1502-1602, and 1802-2002in any of the display systems 800-1300, 1500 and eye-tracking systems1600-200, described above with respect to FIGS. 8-12 and 14-19, mayinclude LC-SRG 2200

In the example shown in FIGS. 22A and 22B, LC-SRG 2300 includes anactive diffraction grating 2302 comprising a surface relief patternformed on the surface of one or both of opposing substrates, and thespaces of the profile may be filled with a birefringent material, forexample, a liquid crystal. In some examples, the orientation of theliquid crystal may be selected by applying a voltage to an electrode, oran electrode pattern, disposed on the substrates.

In the example shown in FIG. 22A, incident light 2308 having a firstlinear polarization may transmits through LC-SRG 2300. The liquidcrystal filling the spaces of active grating 2302 may have an ordinaryrefractive index that substantially matches the index of the surfacerelief profile, and an extraordinary index of refraction mismatched withthe index of the surface relief profile. A voltage may be applied to theelectrodes of LC-SRG 2300, forming and electric field between theopposing substrates with which the liquid crystal may align. In theexample shown, the director of the liquid crystal is aligned by theelectric field to be perpendicular to the substrates and parallel withthe propagation direction of incident light 2308. As such, the effectiveindex of the refraction for incident light 2308 of the liquid crystal isthe ordinary refractive index regardless of the polarization of incidentlight 2308. Therefore, the index of the liquid crystal matches the indexof the surface relief profile, and incident light 2308 transmits throughLC-SRG 2300 without diffraction.

In the example shown in FIG. 22B, a voltage is not applied to theelectrodes of LC-SRG 2300, and the liquid crystal is aligned with itspreferential alignment. In the example shown, the preferential alignmentis along the grooves of the surface relief profile, e.g. parallel to they-axis. For incident light 2308 having a first linear polarizationparallel to the director of the liquid crystal, e.g. along the y-axis,the effective index of the liquid crystal will be the extraordinaryindex and mismatched with the index of the surface relief profile. Assuch, incident light 2308 having the first linear polarization willdiffracted and redirected, based on the phase profile pattern resultingfrom the surface relief profile.

In some examples, both LC-SRG 2200 and 2300 may be designed as aRaman-Natt or a Bragg diffraction grating. In some examples, both LC-SRG2200 and 2300 may be either transmissive or reflective, e.g. transmitand redirect (e.g. diffract) at least a portion of incident light orreflect and diffract (e.g., redirect) at least a portion of incidentlight. In some examples, any of the DT-PBS 802-1202, 1502-1602, and1802-2002 in any of the display systems 800-1300, 1500 and eye-trackingsystems 1600-200, described above with respect to FIGS. 8-12 and 15-20,may include LC-SRG 2300.

FIGS. 23A-23F are schematic diagrams illustrating examples of a PBPgrating 2400, a reflective PVG (r-PVG) 2430, and a transmissive PVG(t-PVG) 2460, in accordance with the techniques described in thisdisclosure. Each of PBP grating 2400, r-PVG 2430, and t-PVG 2460 may beconfigured to exhibit polarization sensitive light splitting andredirection, in accordance with the techniques described in thisdisclosure. In some examples, any of the DT-PBS 802-1202, 1502-1602, and1802-2002 in any of the display systems 800-1300, 1500 and eye-trackingsystems 1600-200, described above with respect to FIGS. 8-12 and 15-20,may include PBP grating 2400, r-PVG 2430, and/or t-PVG 2460. Theexamples shown in FIGS. 23A-23F illustrate example diffraction gratingssensitive to circular polarization. For example, PBP 2400, r-PVG 2430,and t-PVG 2460 or PBP 2450 may transmit and redirect light of both rightcircular polarization and left circular polarization in differentdirections, e.g., via different diffraction orders.

FIG. 23A is a cross-sectional schematic diagram illustrating an examplemolecular orientation of PBP grating 2400, in accordance with thetechniques described in this disclosure. FIG. 23B is a cross-sectionalschematic diagram illustrating an example optical response of PBPgrating 2400, in accordance with the techniques described in thisdisclosure. In some examples, PBP grating 2400 is a liquid crystaloptical element that includes one or more layers of liquid crystals. Insome examples, PBP grating 2400 includes a layer of other type ofsubstructures, e.g., nanopillars composed of high refraction indexmaterials.

As shown in FIG. 23A, the orientations of the liquid crystals 2402remain constant along the z-direction. In some examples, PBP grating2400 that has constant orientation along the z-axis and a birefringentthickness (Δn×d) that is ideally half of the designed wavelength, whereΔn is the birefringence of the liquid crystal material and d is thephysical thickness of the liquid crystal material of the PBP lens 2400.In the example shown in FIG. 23A, PBP grating 2400 has a grating pitchΛ, which may be defined as a distance along x-axis at which the azimuthangle of liquid crystals 2402 have rotated 180 degrees from the initialorientation.

In some examples, PBP grating 2400 may have a liquid crystal structurethat is different from the one shown in FIG. 23A. For example, a PBPgrating 2400 may include a double twist liquid crystal structure alongthe z-direction. In another example, a PBP grating may include athree-layer alternate structure along the z-direction in order toprovide achromatic response across a wide spectral range.

As shown in FIG. 23B, PBP grating 2400 may polarize and redirectincident light based on polarization. For example, PBP grating 2400 maysplit, e.g., redirect non-polarized light via redirection based onpolarization. In the examples shown, PBP grating 2400 redirects an LCPportion of incident non-polarized light in a first transmitted directionand redirects an RCP portion of incident non-polarized light in a secondtransmitted direction, thereby polarizing and redirecting incident lightbased on circular polarization.

FIG. 23C is a cross-sectional schematic diagram illustrating an examplemolecular orientation of r-PVG 2430, in accordance with the techniquesdescribed in this disclosure. FIG. 23D is a cross-sectional schematicdiagram illustrating an example optical response of r-PVG 2430, inaccordance with the techniques described in this disclosure. In someexamples, r-PVG 2430 is a liquid crystal optical element that includesone or more layers of liquid crystals. In some examples, r-PVG 2430includes a layer of other type of substructures, e.g., nanopillarscomposed of high refraction index materials.

As shown in FIG. 23C, the orientations of the liquid crystals 2402 maybe slanted, e.g., liquid crystals 2432 may be arranged in a helicalarrangement along the z-direction. In some examples, r-PVG 2430 may beformed via surface mediated photoalignment, e.g., via liquid crystals2432 doped with a chiral dopant additive. In some examples, r-PVG 2430may be a Bragg diffraction grating including a Bragg grating pitchΛ_(B), at angle θ with respect to the surface of r-PVG 2430.

As shown in FIG. 23D, r-PVG 2430 may polarize and redirect incidentlight based on polarization. For example, r-PVG 2430 may split, e.g.,redirect non-polarized light via redirection based on polarization. Inthe examples shown, r-PVG 2430 redirects an LCP portion of incidentnon-polarized light in a first reflected direction and transmits an RCPportion of incident non-polarized light in without redirection, therebypolarizing and splitting incident light based on circular polarization.In other examples, r-PVG 2430 redirects an RCP portion of incidentnon-polarized light in a first reflected direction and transmits an LCPportion of incident non-polarized light in without redirection, therebypolarizing and splitting incident light based on circular polarization.

FIG. 23E is a cross-sectional schematic diagram illustrating an examplemolecular orientation of t-PVG 2460, in accordance with the techniquesdescribed in this disclosure. FIG. 23F is a cross-sectional schematicdiagram illustrating an example optical response of t-PVG 2460, inaccordance with the techniques described in this disclosure. In someexamples, t-PVG 2460 is a liquid crystal optical element that includesone or more layers of liquid crystals. In some examples, t-PVG 2460includes a layer of other type of substructures, e.g., nanopillarscomposed of high refraction index materials.

As shown in FIG. 23E, the orientations of the liquid crystals 2462 maybe slanted, e.g., liquid crystals 2462 may have a constant orientationin a direction θ with respect to the z-axis. In some examples, t-PVG2460 may be formed via bulk mediated photoalignment, e.g., via recordingthe orientation structure in a thick layer of photosensitive LC polymer.In some examples, t-PVG 2460 may be a Bragg diffraction gratingincluding a Bragg grating pitch AB, at angle θ with respect to thesurface of t-PVG 2460.

As shown in FIG. 23F, t-PVG 2460 may polarize and redirect incidentlight based on polarization. For example, t-PVG 2460 may split, e.g.,redirect non-polarized light via redirection based on polarization. Inthe examples shown, t-PVG 2460 redirects an LCP portion of incidentnon-polarized light in a first transmitted direction and transmits anRCP portion of incident non-polarized light in without redirection,thereby polarizing and splitting incident light based on circularpolarization. In other examples, t-PVG 2460 redirects an RCP portion ofincident non-polarized light in a first transmitted direction andtransmits an LCP portion of incident non-polarized light in withoutredirection, thereby polarizing and splitting incident light based oncircular polarization.

FIGS. 24-26 are schematic diagrams illustrating example liquid crystalshutters in combination with a passive diffraction grating, inaccordance with the techniques described in this disclosure. In theexamples shown, a passive diffraction grating may be a LC filled surfacerelief grating (LC-SRG), an H-PDLC gratings, a PVG, a PBP gratings orany other type of polarization sensitive diffraction grating. The liquidcrystal shutters illustrated in FIGS. 24-26 may each be an example of apixelated DT-PBS, such as DT-PBS 1502A and 1502B described above withrespect to FIG. 14.

FIGS. 24A and 24B are schematic diagrams illustrating a switchable,pixelated birefringence type liquid crystal (LC) shutter 2500. In theexamples shown, LC shutter 2500 includes a pair of orthogonalpolarizers, e.g. polarizers 1 and 2, with a LC cell disposed between. Inthe example illustrated in FIG. 24A, incident light 2502 may be of anypolarization or may be randomly polarized, e.g. unpolarized. Incidentlight 2502 passes through polarizer 1 and is then linearly polarized.The LC cell rotates the polarization of the light 90 degrees, and thelight then passes through polarizer 2 with a substantially hightransmission. The dark and bright states can be spatially distributed bypixelation of the shutter. The light from the not shut down sections ofthe light flux is then redirected by passive grating 2504.

In the example illustrated in FIG. 24B, incident light 2502 may be ofany polarization or may be randomly polarized, e.g. unpolarized.Incident light 2502 passes through polarizer 1 and is then linearlypolarized. The LC cell may have a voltage applied to transparentconductors on opposing substrates of the LC cell thereby forming anelectric field between the electrodes and changing the alignment of theliquid crystal. The amount of rotation may be controlled by the voltageapplied. In the example shown, the liquid crystal is rotated such thatthe polarization of the light is not rotated, and the light does notsubstantially transmit through polarizer 2, e.g. is absorbed orreflected based on the type of polarizer. Because shutters of these typecomprise linear polarizers, they may work in combination with thegratings sensitive to linear polarization of light.

FIGS. 25A and 25B are schematic diagrams illustrating a switchable,pixelated guest-host liquid crystal (LC) shutter 2600. In the examplesshown, LC shutter 2600 includes a dichroic dye 2606 dissolved in theliquid crystal 2608 of a liquid crystal cell, and a passive diffractiongrating 2604. The dye molecules (guest) align with the LC molecules(host). The dye causes only a slight absorption when the LC is in afirst state, e.g. with a voltage applied such that the long axis of theliquid crystal is perpendicular to the surfaces of the LC cell (FIG. 25Abright state), and a strong absorption when the LC is in a second state,e.g. without a voltage applied and the long axis of the liquid crystalmolecules is parallel to the plane of the LC cell (FIG. 25B dark state).In some examples, the bright state and the dark state may be reversedfor a LC cell having the opposite anisotropy, e.g. negative as opposedto positive anisotropy.

FIGS. 26A and 26B are schematic diagrams illustrating a switchable,pixelated, scattering liquid crystal (LC) shutter 2700. In the examplesshown, LC shutter 2700 includes a LC scattering cell 2710 and a passivediffraction grating 2704. In some examples, LC scattering cell 2710 maybe a switchable polymer dispersed liquid crystal cell (PDLC). The liquidcrystal may have an ordinary refractive index substantially matched withthe polymer index of refraction of the PDLC, and an extraordinary indexof refraction that is substantially mismatched with the polymer index ofrefraction.

In the example illustrated in FIG. 26A, incident light 2702 may be ofany polarization or may be randomly polarized, e.g. unpolarized. In theexample shown, the director of the liquid crystal in LC scattering cell2710 may aligned along the preferential alignment, e.g., perpendicularto the surfaces of the PDLC (and in the x-y plane). Regardless of thepolarization of incident light 2702, the polarization will beperpendicular to the director of the liquid crystal and the effectiveindex of the LC scattering cell 2710 will be the ordinary refractiveindex and matched to the polymer. As such, incident light 2702 will notbe scattered and will transparently transmit through LC scattering cell2710 and diffract via passive diffraction grating 2704.

In the example illustrated in FIG. 26B, a voltage may be applied totransparent conductors on opposing substrates of the LC scattering cell2710 thereby forming an electric field between the electrodes andchanging the alignment of the liquid crystal. The amount of rotation maybe controlled by the voltage applied. Because the LC droplets may berandomly distributed in the LC scattering cell 2710 volume between thesubstrates, the light 2702 will see a random pattern of mismatched indexinterfaces, and will scatter randomly, including backscatter, and thetransmission of incident light 2702 will be substantially reduced.

As described by way of various examples herein, the techniques of thedisclosure may include or be implemented in conjunction with anartificial reality system. As described, artificial reality is a form ofreality that has been adjusted in some manner before presentation to auser, which may include, e.g., a virtual reality (VR), an augmentedreality (AR), a mixed reality (MR), a hybrid reality, or somecombination and/or derivatives thereof. Artificial reality content mayinclude completely generated content or generated content combined withcaptured content (e.g., real-world photographs or videos). Theartificial reality content may include video, audio, haptic feedback, orsome combination thereof, and any of which may be presented in a singlechannel or in multiple channels (such as stereo video that produces athree-dimensional effect to the viewer). Additionally, in someembodiments, artificial reality may be associated with applications,products, accessories, services, or some combination thereof, that are,e.g., used to create content in an artificial reality and/or used in(e.g., perform activities in) an artificial reality. The artificialreality system that provides the artificial reality content may beimplemented on various platforms, including a head-mounted device (HMD)connected to a host computer system, a standalone HMD, a mobile deviceor computing system, or any other hardware platform capable of providingartificial reality content to one or more viewers.

The techniques described in this disclosure may be implemented, at leastin part, in hardware, software, firmware or any combination thereof. Forexample, various aspects of the described techniques may be implementedwithin one or more processors, including one or more microprocessors,DSPs, application specific integrated circuits (ASICs), fieldprogrammable gate arrays (FPGAs), or any other equivalent integrated ordiscrete logic circuitry, as well as any combinations of suchcomponents. The term “processor” or “processing circuitry” may generallyrefer to any of the foregoing logic circuitry, alone or in combinationwith other logic circuitry, or any other equivalent circuitry. A controlunit comprising hardware may also perform one or more of the techniquesof this disclosure.

Such hardware, software, and firmware may be implemented within the samedevice or within separate devices to support the various operations andfunctions described in this disclosure. In addition, any of thedescribed units, modules or components may be implemented together orseparately as discrete but interoperable logic devices. Depiction ofdifferent features as modules or units is intended to highlightdifferent functional aspects and does not necessarily imply that suchmodules or units must be realized by separate hardware or softwarecomponents. Rather, functionality associated with one or more modules orunits may be performed by separate hardware or software components orintegrated within common or separate hardware or software components.

The techniques described in this disclosure may also be embodied orencoded in a computer-readable medium, such as a computer-readablestorage medium, containing instructions. Instructions embedded orencoded in a computer-readable storage medium may cause a programmableprocessor, or other processor, to perform the method, e.g., when theinstructions are executed. Computer readable storage media may includerandom access memory (RAM), read only memory (ROM), programmable readonly memory (PROM), erasable programmable read only memory (EPROM),electronically erasable programmable read only memory (EEPROM), flashmemory, a hard disk, a CD-ROM, a floppy disk, a cassette, magneticmedia, optical media, or other computer readable media.

As described by way of various examples herein, the techniques of thedisclosure may include or be implemented in conjunction with anartificial reality system. As described, artificial reality is a form ofreality that has been adjusted in some manner before presentation to auser, which may include, e.g., a virtual reality (VR), an augmentedreality (AR), a mixed reality (MR), a hybrid reality, or somecombination and/or derivatives thereof. Artificial reality content mayinclude completely generated content or generated content combined withcaptured content (e.g., real-world photographs). The artificial realitycontent may include video, audio, haptic feedback, or some combinationthereof, and any of which may be presented in a single channel or inmultiple channels (such as stereo video that produces athree-dimensional effect to the viewer). Additionally, in someembodiments, artificial reality may be associated with applications,products, accessories, services, or some combination thereof, that are,e.g., used to create content in an artificial reality and/or used in(e.g., perform activities in) an artificial reality. The artificialreality system that provides the artificial reality content may beimplemented on various platforms, including a head mounted device (HMD)connected to a host computer system, a standalone HMD, a mobile deviceor computing system, or any other hardware platform capable of providingartificial reality content to one or more viewers.

What is claimed is:
 1. An eye-tracking optical assembly comprising: alight source for illuminating an eye; a first diffraction typepolarizing beam splitter (DT-PBS); and a second DT-PBS, wherein thefirst DT-PBS is configured to direct, based on polarization, a firstportion of light from the second DT-PBS towards an eye-trackingdetector.
 2. The eye-tracking optical assembly of claim 1, wherein thesecond DT-PBS is configured to direct, based on polarization, the firstportion state of light towards the first DT-PBS.
 3. The eye-trackingoptical assembly of claim 1, wherein one of the first DT-PBS and thesecond DT-PBS is configured to compensate for a spectral dispersion ofone other of the first DT-PBS and the second DT-PBS.
 4. The eye-trackingoptical assembly of claim 1, wherein at least one of the first andsecond DT-PBS comprise a reflective or transmissive polarization volumegrating, PBP grating, a liquid crystal filled surface relief grating, ora holographic polymer dispersed liquid crystal grating.
 5. Theeye-tracking optical assembly of claim 1, wherein at least one of thefirst and second DT-PBS reflect and direct, based on polarization, thefirst portion of light.
 6. The eye-tracking optical assembly of claim 1,wherein at least one of the first and second DT-PBS transmit and direct,based on polarization, the first portion of light.
 7. The eye-trackingoptical assembly of claim 1, wherein at least one of the first andsecond DT-PBS is configured with optical power to converge or divergelight.
 8. The eye-tracking optical assembly of claim 1, wherein thesecond DT-PBS is configured to direct, based on polarization, the firstportion of light towards an eye.
 9. A head-mounted display (HMD)comprising: a light source for illuminating an eye; a first diffractiontype polarizing beam splitter (DT-PBS) configured to direct, based onpolarization, a first portion of light from a second DT-PBS towards aneye-tracking detector.
 10. The HMD of claim 9, wherein the second DT-PBSis configured to direct, based on polarization, the first portion oflight towards the first DT-PBS.
 11. The HMD of claim 9, wherein one ofthe first DT-PBS and the second DT-PBS is configured to compensate for aspectral dispersion of one other of the first DT-PBS and the secondDT-PBS.
 12. The HMD of claim 9, wherein at least one of the first andsecond DT-PBS comprise one of a reflective or transmissive polarizationvolume grating, PBP grating, a liquid crystal filled surface reliefgrating, or a holographic polymer dispersed liquid crystal grating. 13.The HMD of claim 9, wherein at least one of the first and second DT-PBSreflect and direct, based on polarization, the first portion of light.14. The HMD of claim 9, wherein at least one of the first and secondDT-PBS transmit and direct, based on polarization, the first portion oflight.
 15. The HMD of claim 9, wherein at least one of the first andsecond DT-PBS is configured with optical power to converge or divergelight.
 16. The HMD of claim 9, wherein the second DT-PBS is configuredto direct, based on polarization, the first portion of light towards aneye.
 17. A method of tracking one and/or both eyes of an HMD usercomprising: directing light from a light source towards a user's eye;reflecting the light from the user's eye towards a first diffractiontype polarizing beam splitter (DT-PBS); directing, based onpolarization, a first portion of the light from the first DT-PBS towardsa second DT-PBS; and directing, based on polarization, the first portionof the light from the second DT-PBS towards a detector.
 18. The methodof claim 17, wherein the light from the light source is broadband. 19.The method of claim 17, wherein at least one of the first and secondDT-PBS is configured to reflect and direct, based on polarization, thefirst portion of the light.
 20. The method of claim 17, wherein at leastone of the first and second DT-PBS is configured to transmit and direct,based on polarization, the first portion of the light.